After doing a quick market research (on eBay) for you, here's what we can say about your planned venture:
1) Competition - Currently the competition is quite high. In fact the market seems a bit saturated at the moment, although this may change as market trends always do change.
2) Demand - Currently the demand is way below 50%. For you have a good chance, the product should at least have a potential market demand of 60%. It may work if the closing prices are high, but then again that too is quite low.
3) Oil paintings is a broad category, so you may find that there is quite a bit of variation: paintings from some different periods and of different subjects might do better than others
Another thing to consider is, for a market like this you would need quite a bit of knowledge to make it work, like you would need to know a lot about art to pick paintings that would sell really well.
Also you mentioned that you already have a supplier in mind, a Chinese one. We now know that the market for oil paintings isn't that good plus if your customers know that you source these paintings from China, it may well lower your chances of a sale. (People don't tend to associate products from Asia with high quality, so this may have an impact on your success too)
Although this may work for you if your were selling at a market or car boot sale, where people are more likely to buy a bit of (low quality) art for $70 or something.
Hope this helps. Cheers!