This thread is kind of all over the range of things. Do not do it because you can get everything you will offer at box stores, to not to do it because there are others doing it already.
I think what you would really need to consider it what type of business are you going to target. Construction companies would want grease and cutting/grinding equipment, maybe come winter some painting supplies. You know to kind of fully maintain equipment while it is down seasonably.
Body shops, would want strippers, paper goods, adhesives, masking products. Throw in a few bulbs, some wiring products, and a few more lines.
A repair shop could be all of the above. Plus fender/seat protection, and the list goes on.
Know the business you are going after and get the best of the products you can offer that business.
I am not sure I would be going after much earn as you pay business. I think that maybe OK for the middle man in the end, but boy you are sticking it out there aways to get that. You would have to buy from different vendors and likely not getting a real great discount, because you would be stretched out dealing with a few. Instead of just one.
Then you would be getting paid on time after you have paid in full. I think where tool companies kind of have a niche in this is you can buy gearwrench from numerous places, but you can only buy mac and SO from a certain place. Besides that is their business model, so they kind of help the franchise guy get there.
You could also partner with some one that is kind of offering some of what you want to sell. Say the independent parts store has paper products or grinding product. He does not sell a bunch, but enough to keep it around. If you could buy your product from him, he buys more and gets better discounts, that he can pass on to you, and make more money on his walk in guys.
Same true with grease and lubricants. Maybe the little distributor that you can sell their products and and they help you out in the end.
Sort of like a salesman that is selling their products, but doing it for yourself. Their products are getting out and they get better deals because of it.
Having an exit strategy is not a bad thing. Unloading consumables would be tough. Not many out there wanting everything, and likely having to much for any one to want it all.
I am not sure how long you would want to put into this. I could see it certainly taking a while to get it up and going. Even longer in getting it to the point of being able to make a living. Even longer yet, before you could start buying and selling enough to get larger discounts and selling at bigger margins.
One last thing to say. It will not be easy. Any one in business will tell you that. If you want to just be a part time thing or not take it to seriously, or not have the time to get it going, do not do it. Money aside, and you will need plenty of that, you are kind of creating a need for your business. To be successful you will have to pitch that to you buyers first and vendors later.