help with multipe blogs

Hey,

I'm sure this has been covered before, so i apologies in advance but i wasn't able to find the answers to a few of my questions.

I currently have a blog and I'm looking at re-creating it on different domain names to inevitably get more visitors to my pages.

I'm wondering how the best way to go about this is..

1. Should my domain named be http://www.mydomain.com or is it just as fine to have a http://www.mydomain.wordpress.com domain name?

2. Is it best to alter the template theme of each new blog created? So that they look different but contain the same information, instead of having people potentially view the multiple sites and feel they are always landing on the same one?

3. I've noticed a few posts on free plugins to assist in up-loading posts to all blogs at the one time. I've been looking at the feedwordpress and was wondering if someone could tell me a bit more how this actually works. Once installed will i need to have all my domain names within the one admin (dashboard) area?

Thanks in advance for any help

Shorter domain is generally better, plus the more complicated the more difficult for folks to remember.
I would say go for slightly different themes personally.