Now I don't do decorating but would assume start off with the minimum, then as your business grows,
grow your balloon kit accordingly.

I would assume a sizer is a must and an electric pump, will you use helium or go all air filled?
Some knot stands from Ikea and the loomie stands for table stands, balloon wise buy in as required.

Try to sell so that you do not need one balloon out of a bag of 100, buy in 25 count bags.