I only have 1 iphone, but it is on a t-mobile USA pre-paid plan, so I have no data plan. So that's close to what you want to do with your 2nd one. It works great for me, and my monthly charges are very low as a very light phone/sms user.

Wifi at home and when traveling is more than enough. You can sync it with outlook using itunes. I used to do that, but ended up switching over to exchange server sync with google (cal, mail & contacts) which turns out to be a much better option for me, since I was already keeping my calendar and some email on google anyway.

-David