I want to lunch affiliate site. Need to select Domain as my targeted product? Short or Long domain name which one effective?
In most cases, you should try to get an EMD (Exact Match Domaim) when available. For instance, if you are promoting 'Blue Shoe Horns', an ideal domain would be BlueShoeHorns.com. If the .com is gone, a .net should work just fine too. While it may not be as valuable if you ever want to resell the domain/site (without taking traffic, links, revenue into consideration), the .net extension still ranks well in Google in my experience. Short, brandable domains are great if you plan on trying to grow a business around that specific brand. But, you will have to do more 'work' as far as SEO goes. When it comes to length, try to keep it as short as possible while still getting your keywords in the domain. Avoid having words like 'the', 'and', 'my', etc.. in the domain.
Nothing, domains are not case-sensitive. I suggest you do a lot more reading and research before starting this endeavor.