Its a good idea to do, but its just one factor amongst many.
If you choose a long tail search centric domain name, you will probably loose memorability from your users. That wont be an issue if you do not expect to get repeat customers but only drive customers to a single sale website. So in the end it comes down to your intended use. Hard to give you recommendations without knowing that.
Yes Definitely you ought to check for the availability of domain name. These days its hard to get a domain name of choice. But if you want a domain name which is firstly a name of your choice, is cheap and secure at the same time then you can go for .ooo domain name. Get this global domain name with many benefits.
Lol are you serious?! An ooo domain would be as appalling, even moreso, than the plethora of rapidly failing new extensions already around. Expect to see half of them gone within the next couple of years. People my advice is AVOID any extension not established and especially any that are just being marketed now. The only people you are going to make rich are the registrars and their resellers.