I was a general manager for a miniatures company for awhile and learned quite a bit about the industry in my time.
GW is the big player on the block, but you'll find hordes that are ready to convert (to another game system) just so they can stick it to GW. There is a lot of money in the minis market- unfortunately GW takes most of it...
I think another player in the plastic mini market would do well, but as mentioned earlier by Pogre, the set-up costs are extremely high. If you do decide to go metal, make sure you find a good quality metal- not all white metals are made equal. We went through quite a few before finding the right mixture that made production much more efficient and the product looked a hundred times better. Casting equipment is better if puchased used- much cheaper and the caster, vulcanizers (for making molds) and melting pots are usually built like tanks- they can take a beating and keep on working.
See if you can talk to the big distributors ahead of time and establish relationships with them. It's a hard-going if you decide to go direct to retailers with your product as opposed to working with the major distributors to get your product into stores. Don't get me wrong- distributors are not going to make you rich, but they will make it easier to get into stores. Many retailers simply will not buy your product from you if they can't get it from their distributor, even if they love it. The big distributors are Alliance and ACD. There are a few smaller ones that are worth looking into, but those two are the titans. Of course this touches on one of the paradoxes of selling your game, many stores won't stock your game if there is no demand- but there can't be demand for something that gamers don't know anything about. Of course, that's where your marketing campaign will have to come in.
That's all I can think of for right now, I'd be happy to answer any specific questions you might have.
Good luck!