Welcome to the site. You can get more design related info in the Layout design forum. I think there has already been some posts there.
As far as where to get trains, it depends on what you want. Is there a specific scale/period/locale that you are interested in?
I for one have an interest in 1960s-present Germany in N scale, so there are tons of options available - there is a local shop that is well stocked, and there are numerous Internet mail order companies that cater to that as well. And let's not forget eBay.