Welcome to the Geeks.
I would never sell the products you use to detail their car. Your giving away your trade secrets. Not that it matters 90% of detailing is technique.
I would keep your supplies to a bare minimum. Less is more. Try and find multi-purpose products like Ultima WW+ or my preference Garry Dean's Detail Juice. They both do the following, rinse less wash, exterior QD, Interior QD, Clay Lube, Tire treatments and water softener. The are both highly concentrated so a couple of ounces will make one gallon of usable product.
I'm Chemical Guys fan. Their prices are very reasonable. A lot of there products can be diluted. So more bang for your buck. They also sell in gallons so yeah your saving a lot of money buying bulk. I do use other brands.(BF, Optimum, Menzerna.) CG's Jetseal is a little pricey but is really good I prefer M-Seal anyway, BF Wet Diamond All Paint Protection is also good. CG make two paste waxes Pete's 53 and 50/50 reasonably priced. They both have nice longevity when layered over a sealant. If you can get a little higher priced waxes Bouncer's Vanilla Ice for longevity an looks.
My advice. Do your research. Find as multi use products as possible. I'd rather spend $50 on one highly concentrated product that does a lot of things really well then 5 things that have one purpose. Products you will burn threw are QD's, clay lube, APC's, Fabric cleaners, wheel cleaners and brushes.
Read reviews directions how to use. Price is always a consideration.
What will give the most headaches are wheel cleaners, wheel brushes, So you end up having a wheel cleaner and a couple of APC's as back ups for the really bad rims. As far as glass cleaning go right to Car Pro and pick up the fast glass towels no cleaners needed.
Just an FYI:
All clay bars sold in the US are made by the same company because of patent law and sold to the retailers. The patent for clay sold outside of the US is held by a Japanese company. So as long as you are buying branded retail names you are getting the same stuff. So get the biggest bar for the money. CG has pretty big bars for the price and they run a lot of clay bar specials.