Alot of the things on your list are kind of over kill.
A efficient grooming kit really just needs a curry (different kinds), a hard brush, a soft brush, and a hoof pick.
Halters, and boots etc. Come in different sizes so unless your going to carry this stuff around with you shopping for horses and just by the one that fits into it, you should by them after.
What are you planning on doing ? Seems like something fancy?
Do you already have a horse in mind that your shopping for?
you can save 80 + dollars wrapping those polo wraps on your horses legs then going out and buying shipping boots.
Not all horses over reach which is what bell boots are for (as far as I understand them)
Socks make great tail bags.