I have been making chocolates/bon bons/pralines for a little over a year, but can offer a bit of advice-based on my positive and negative experiences--on molds. At first I didn't realize that the molds differed considerably in what size finished piece they turn out, and as a result, I initially purchased some quite small molds. A lot of people like smaller chocolates, but I found them difficult to fill and too small to provide a good taste of the filling (perhaps I am just making excuses for gluttony!). Then I learned that many manufacturers provide a guide to size by specifying the weight of the finished chocolate. I find this guide counterintuitive--it's the volume of the cavity one cares about, not the weight of the product, and nobody has explained what they weighed to determine the figure (is it the weight of a piece of solid dark chocolate or ...?)--but weight is all there is to go on and it does provide a useful aid. I have found that weights between 11 and 16 grams per piece work best for me. I have some dome-shaped molds that hold 18g, and they are particularly good for two-layer pralines or one that has a whole hazelnut submerged in a praline filling. So far no recipient has complained about the larger size, and these do not look out of proportion in a box with smaller pieces.
In the U.S. I have bought online from J.B. Prince in NYC, Tomric in Buffalo, NY, and Chef Rubber in Las Vegas. Bakedeco.com also has lots of molds, but their images are very small. J.B. Prince has good prices and quick service, but they do not provide weights to help (that's how I ended up with small molds in the beginning). Tomric has a very large selection, and they carry (or can obtain) anything from chocolateworld.be in Belgium. BUT--and it can be a big issue--most Chocolate World molds take at least the 3-4 weeks stated on the Tomric website to arrive, or longer. Just remember that when you shop online, don't go by how large or small the mold looks in the image.
As for purchasing chocolate, I use chocosphere.com. They have a huge selection and carry just about every mainstream chocolate. They also sell smaller amounts (such as 1 Kg bags) so it's possible to try various options without breaking the bank. They have good customer service and quick delivery. I have also bought from Gygi (but, as Ruth said, only Callebaut). Worldwidechocolate.com is very similar to Chocosphere in their offerings; they have free shipping on orders over $99, but the base prices are a bit higher than Chocosphere's. Their offerings are, in my opinion, somewhat more limited than Chocosphere's (for example, World Wide Chocolate does not carry 1-Kg blocks of Amedei and does not have Felchlin at all).
I think Callebaut would be a good chocolate to start. Look at their website to decide among all the choices, and note the drops system that tells you how viscous the chocolate will be when melted.