Horse Boots Set

I am getting a horse soon (a dutch warmblood if it helps) and I plan to do light showing, but regular riding with him. I ride english and jump, and I already have stuff like a Saddle, bridle, saddle pad, grooming kit, and et cetera.
My main questions are:

I also live in a place with cold but never below 0 winters. Should I invest in a blanket?

Do I need a whole new set of brushes or just clean them with warm water??

Should I get new saddle pads or just wash them well?

and finally:

Do I need anything else besides a saddle, bridle, saddle pads, grooming kit, flyspray, jump/bell boots, and some horse shampoos?
edited: I am boarding my horse at a private, family-owned barn. I know what is poisonus and such, and I've been riding since I was 6, so I know a lot. I'm all prepared in terms of boarding, trailering, farrier services, vaccinations, vet services, and deworming.