I want to sell my fine art photography online and also offer my training services for photographers (videos,books,workshops, etc). In trying to build a brand would it be best to have 2 separate sites or can I tastefully combine both as 1? In regards to SEO Does it matter if I have two different customer types & businesses on 1 site (people that buy pictures & people that want to make pictures)?
My best advice is to maintain everything under one same roof, since all your services are somehow topically related to each other. It would be different if you were selling unrelated products and services and, then, in that case, you would need separate sites.
No matter how many lines of businesses you run (again, within the same industry), you may want to build up authority for the main domain, in a way that all your pages benefit from that. Focus on creating an intelligible and logical content tree, so the areas of the website are well differentiated, including a hierarchical URL taxonomy that both users and Search Engines can understand.
Sounds like your business is very similar to some existing marketplaces. See Voice123.com, for voice over talents. They offer a large database of voice artists, and at the same time they connect them to customers that are companies searching for voice overs.
Hope this helps.