The shogun starts pretty strong in 1453. I suggest two options:
- start on the bookmarked 1470s date when the shogun is weaker;
- don't be the nail that gets hammered down! Let the shogun lose power and authority crushing other daimyos who get ideas above their station while you lie low and consolidate your position. Maybe even try and get in the shogun's favour so that he may give you provinces! But wait until he is weak before resorting to open aggression.