Starting a blog

Good afternoon all,
I have just a few questions.

I have a niche I want to go after, not sure if it will produce as big as I like, so want to start a bit smaller to test.

Do you recommend
1) Using WP with your own domain name? or
2) Using just WP without your own domain-- I.e. wordpress.com/XXXXXX

Also, do you recommend staying with .com or will any other address endings work?

If you just want to test it I would use a blogger blog where you can easily ad adsense to it if you want. I think blogger blogs are a good place to market test. If this is something you are wanting to build a big project of, I would use your own domain so you have the control. As far as domains. If you are going to be making a flagship blog, I would use a .com if it is just going to be a small niche site I would use a .info

I like to test a niche with squidoo.