I think leading, grooming, handling feet is all that is necessary. Anything else is just icing on the cake.
My 3 month old colt leads well & sets up square, stands for the farrier, has been bathed & introduced to the clippers, behaves for dewormer, loads easily, and will be learning to tie in the next couple weeks.
My yearling filly, all of the above but has been clipped, lunges, works in hand through & over all of my trail class obstacles, has been sacked out, has had the very light pony saddle on her back a few times, rope work especially on legs, and we've played doctoring - wrapping legs, etc. so it won't be something new should she get hurt and need actual care.
Not enough is a bad thing and too much can be just as much if not more of a bad thing. If it's done right the extras aren't a bad thing, but if not done the right way they can be spoiled monsters! Unhandled weanlings doesn't bother me much, but by the time they are yearlings they should have basic handling & ground manners.
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.