An enigmatic pilgrimage

Question

This puzzle is a bit complex, so I'll explain the steps:

1. The first part is composed of four mini-puzzles. Each of them has a different key to make it a little harder to reach the solution, I think the difficulty increases with each puzzle, but that might be subjective.
2. Each puzzle starts from the "left", so there are two arms which are the hints, and the final arm which is the solution. The circle in the center shows how the four puzzles are positioned (the colored arc covers the three arms of each puzzle).
3. If a mini-puzzle explicitly shows an operation, then that should be used, otherwise it means the key is to be found elsewhere (you'll love to hate me).
4. Once all four puzzles are solved, you should have four separate "clues". The order of the solutions is important for the final solution, but the puzzles can be safely solved in any order as they are independent from each other.
5. The riddle is the last part of this complex puzzle, which will help you reach the final solution. Beware of puns and word plays!
6. The solution to this question is a single word.
7. All of the four solutions are required to reach the final answer, therefore the riddles applies to all of them equally.

Hint:

The riddle does apply to all four clues equally, but they will not change, while simultaneously changing a bit. The riddle is something "extra".

Second hint:

The riddle and its lines have been separated different stanzas for a reason.

Third hint:

When you get to the end of the riddle, it might help to think out loud.

Four mini-puzzles

                       

Riddle

Four clues you have discovered,  
    to reveal what you seek,  
but soon they'll be remodeled,  
    to make them even more unique.  

It takes you to start the sequence,  
    but make sure you're not misled,  
two of them are sequins,  
    pick the last and go ahead.  

But then next in line,  
    here comes an addition,  
an indeed positive sign,  
    in the middle of Charing's station.  

And finally there's a pair,  
     if they're leading, they don't count,  
but now you must beware,  
    their position is paramount.  

Now put them all in order,  
    in the same one that was showed,  
if everything was proper,  
    you'll decipher the unique code.

---

^{notate bene: both the graphic puzzle and the riddle have been created by me. Good luck and have fun.}

Answer 1

The four mini-puzzles

1. Solved by Arbitrary Kangaroo:

   to convert the letters to numbers and subtract: 8O-9A=815-91=724=7X and 2S-9I=219-99=120=1T. So the final answer is 1Z-7E=126-75=51=5A.

2. This and 3 are taken from rand al'thor:

   Blue triangle times red circle equals 20, so these two shapes should be 4 and 5. Green square times blue triangle equals 52, so these two shapes should be 4 and 13. So blue triangle is 4, red circle is 5, green square is 13, and the final answer is 5 times 13 equals 65.

3. The Z's seem to be irrelevant: on the periodic table, Mn is manganese, number 25, and Tc is technetium, number 43. So the final answer is rhenium, number 75.

4. Inspired by Sconibulus,

   just take every third prime: 2, 7, 17 are the 1st, 4th, and 7th primes and 19, 31, 43 are the 8th, 11th, and 14th. So the final answer is 73, the 21st prime following the 15th and 18th.

So the four answers are

5A, 65, 75, 73.

The riddle

Four clues you have discovered,
to reveal what you seek,
but soon they'll be remodeled,
to make them even more unique.

Introduction, this means that we will make slight modifications to the answers of the four puzzles to get our final answer.

It takes you to start the sequence,
but make sure you're not misled,
two of them are sequins,
pick the last and go ahead.

Idea taken from @rand al'thor:

We need "you" to start the sequence, but the first two letters are only decorations, as "U" would be pronounced the same (and it's the last of the set).

But then next in line,
here comes an addition,
an indeed positive sign,
in the middle of Charing's station.

I suspect this refers literally to the character "+", as the station is named "Charing Cross".

And finally there's a pair,
if they're leading, they don't count,
but now you must beware,
their position is paramount.

This stanza refers to a pair of zeros: they usually don't count when they're in a leading position, but here they're necessary.

Now put them all in order,
in the same one that was showed,
if everything was proper,
you'll decipher the unique code.

We need to prepend U+00 to the answers of the four mini-puzzles to get U+005A, U+0065, U+0075, U+0073. This is unique code, I mean, unicode for the word Zeus.

Answer 2

Partial answer (work in progress)

The four mini-puzzles

1. Thanks to Arbitrary Kangaroo, the algorithm seems to be

   to convert the letters to numbers and subtract: 8O-9A=815-91=724=7X and 2S-9I=219-99=120=1T. So the final answer is 1Z-7E=126-75=51=5A.

2. Blue triangle times red circle equals 20, so these two shapes should be 4 and 5. Green square times blue triangle equals 52, so these two shapes should be 4 and 13. So blue triangle is 4, red circle is 5, green square is 13, and the final answer is 5 times 13 equals 65.

3. The Z's seem to be irrelevant: on the periodic table, Mn is manganese, number 25, and Tc is technetium, number 43. So the final answer is rhenium, number 75.

4. Inspired by Sconibulus,

   just take every third prime: 2, 7, 17 are the 1st, 4th, and 7th primes and 19, 31, 43 are the 8th, 11th, and 14th. So the final answer is 73, the 21st prime following the 15th and 18th.

So the four answers are

5A, 65, 75, 73.

The riddle

Four clues you have discovered,
to reveal what you seek,
but soon they'll be remodeled,
to make them even more unique.

I suspect the final answer is UNIQUE - very sneaky, Alenanno! But I may be wrong - this is just a hunch.

It takes you to start the sequence,
but make sure you're not misled,
two of them are sequins,
pick the last and go ahead.

Start with the word "you", and notice that it's pronounced the same as U, so the letters Y and O are essentially useless - just 'decorative' letters. The OP has said that "sequins" are meant to be "shiny decorations", so perhaps the two letters Y and O are our sequins, and "the last" is U.

But then next in line,
here comes an addition,
an indeed positive sign,
in the middle of Charing's station.

Addition and "positive sign" probably refers to +, and the letter most similar to that is T. Also Charing's station is Charing Cross, and the middle of this word is O.

And finally there's a pair,
if they're leading, they don't count,
but now you must beware,
their position is paramount.

The two possible 'pairs' among the four mini-solutions are (65,75) and (73,75). The reference to "leading" suggests we should take (73,75) and discard the (identical) leading digits.

Now put them all in order,
in the same one that was showed,
if everything was proper,
you'll decipher the unique code.

Again, I think this may signal that the final solution is UNIQUE.

Answer 3

Puzzle 1:

A possible answer is 9+8 = 10+7, O(15)-A(1)=14+10=X(24). That means 9+2= 10+1, 19(S)-9(I) +10 = 20(T) and 7+1 = 26(Z) - 5(E) = 21(U) for a final answer of 8U

Puzzle 2:

Common factors of 20 and 52 are 4,2,1. Triangle is one of these, making the result 65, 130, or 260 (probably 65, as it's 2 digits like everything else)

Puzzle 3:

Z is constant, Atomic number of the other element always matches the result number, 75.

Puzzle 4:

Seems to be related to primes, 2,7,17 are 1st, 4th, 7th primes, 19, 31, 43 are 8th, 11th, 14th primes. That leaves 47,61,73 for the 15th, 18th, and 21st primes. Making the answer 73.

Now we have potential solutions to every subproblem, and must tackle the riddle:

It takes you to start the sequence,  
but make sure you're not misled,  

Puzzle 1 answer has U in it. So it comes first

And finally there's a pair,  
 if they're leading, they don't count,  
but now you must beware,  
their position is paramount. 

We have two pairs, 73 and 75 both pair the leading 7, but 75 and 65 both pair the trailing five. "If they're leading, they don't count" implies that the pair we want is 65, 75.

...but I can't make heads or tails of the rest yet