I think I've got the overall answer, but I'm missing substantial parts of the first stanza.
The answer is:
Three two and five versus one five and three twos,
sellable merchandise made out of these clues,
The "sellable merchandise" are products. The products of the numbers in the first line are 3 × 2 × 5= 30 and 1 × 5 × 2 × 2 × 2 = 40.
latter being northern the first's in the east,
This line tells us to treat these numbers as latitude and longitude, 40° N and 30° E. This is a location in Anatolia.
country's name one thousand years back at least.
Or Asia Minor, as it was called earlier. 1,000 yeaars ago, it was part of the Byzantine Empire, whose capital was Constantinople, today's Istanbul.
Find out the year when that state found its winner,
Constantinople was conquered by the Ottoman Empire in 1453.
then pick a Roman wife but no beginner,
Uxor means wife in Latin. Without its first letter, we get xor.
take her out somewhere for coffee or tea,
To a café, that is.
our destination's a quite well-known sea.
Xor is not a part of the solution, it is the bitwise exclusive or. The operands are 1453 and cafe, but both interpreted as hexadecimal. (That's 5,203 and 51,966 in decimal.) We get:
1453 xor cafe = dead.