The number one thing you missed is what cell carrier are you using and where are you located? You need to pick one that has the coverage where you need it - where you live, work, travel and play. And don't say and/or assume it doesn't matter or they all provide service where you plan to use the device. Do your homework and make sure.
All applications drain the battery. No way around that one.
BB email works as you wish, but only with a BB data plan. BBM is only on the BB and only if you have the BB data plan. No way around that either. If you want an iPhone-like browser and Internet, then get an iPhone.
The second part of your post concerning minutes, rollover and data is dependent on the carrier you chose and the plans they offer. Has little to do with the phone you buy.