Starting out, just use Aweber. They got everything you need. How often to send to your list will depend on your specific relationship to them and what you're sending in your messages. So the answer is test and watch the percentage of opens you get in Aweber. I send messages usually 3-4 times/week otherwise I see the percentage of "opens"" go down.

I can say that you don't want to spread out your messages too far (week or longer) as your lists will become less responsive to you.