Keywords for Amazon affiliate website...?!

Hello friends and best wishes to everyone!!!

I'm considering to create an Amazon affiliate website for me. I have one old domain, i know the niche and i know how to create a website, but those bloody keywords are black holes for me, so if i eventually make that site ill pay for some keyword service of course...
My problem is that i don't know what kind of keywords i should be looking for, how many of them to start, to put them in the posts, titles, etc...?!
Second, is it a good idea to make a Blog page where all the posts will be located...?!

Thanks and cheers