Well, most of the suppliers have been identified. As for inventory, as them for their recommendations. They'll usually supply you with a spreadsheet of what to get to start out. LD Carlson provides one of the better ones.
However, they all push stuff that really isn't needed along with the key items you should have. Beware of the wine kits. Those are generally slow movers with a big up front costs. Also ask yourself "what do most people commonly buy online?" vs. stuff that's more commonly bought at a "brick and mortar" store. Heavy items are usually bought locally vs. light weight items that ship free etc. Like all things there are exceptions.
I would say initially focus on the essentials and start adding all the cool stuff as you grow. i.e. You need a good malt selection, a reasonable hop selection, a good yeast selection, and key cleaning/sanitization & equipment items like PBW, Starsan, hydrometers, bottle caps etc. Things like Blichman items, pumps etc. can come later if you determine there is a market for it.
I would also recommend contacting and seeing if you can work for a homebrew store that won't be in your competitive area. Some owners are really nice and helpful...others are...well...you know.
In general, I'd say you have a lot of homework to do; a lot of digging and research. If you don't have any small business experience, especially retail hobby business exp. (besides being a shelf stocker at your local mart...), follow up with your local small business association. If there's a SCORE chapter near you, even better and check that out too.
As for start up expense and revenue - you can find that/figure it out on your own. Again, your local SBA or SCORE chapter will really help you out a lot.