I believe the word being clued here is:
My prefix is big in the Middle,
An ENT is a big tree-like creature in JRR Tolkien's Lord of the Rings, which is set in Middle Earth.
my infix is found at the end,
A TAIL is found at the end of an animal, vehicle or other object.
my suffix was once at the front,
Something which LED was once at the front (e.g. of a race, a team, a tribe, etc.).
my whole is what is involved.
The word ENTAILED is a synonym for involved.
As for the hints:
1. The word 'ENTAILED' has two anagrams: DATELINE and LINEATED, which are represented here using the day's date with lines added...
2. An alternative prefix could be EN, one of the middle letters of the English alphabet (which is centred around M and N).