First, you are going to have to pay for a data plan. This is not a 'voice plan only' option - it doesn't work that way. One of the reasons is that that data portion is not connection based, but packet based so they really cant appropriately charge you 'per minute' like they can do with a phone call or even an SMS. To do push mail properly, you need the packet data - BlackBerry advertizes as "always on, always connected' and you can only do that on packet data.
BTW, get used to it - the carriers are looking for new revenue streams past voice and data is going to cost you whatever the source. They are also expecting that with new networks you will pay from everything from browsing, tv, DVD, music, tickets, GPS services, email, video calls, IM, etc, etc... In fact they are counting on this.
So in short:
1. No, but you there are plans out there less then $50. Use it for a couple of months and you find this is a HUGE bargain. It might not seem so from where you are today, but then you haven't used a BlackBerry yet. If you can manage your business by email also, it is possible that your voice minutes will drop as well.
2. Personally I don't think the footprint is that much different. In fact I would day the BlackBerry is easier to carry on a day-to-day all day long basis. Especially in the case of Verizon, the phone on the BB is very, very good. I do prefer to use a Bluetooth headset but I find the handset itself is pretty good up against the ear.
3. Right. This is very much a business focused device. Yes, the device is incredibly stable. SpeakerPhone is not available on Verizon yet, but maybe in the future.
4. BT works very, very well for the BlackBerry as long as you are looking for just the headset and handsfree profiles. RIM is very security conscious and is not enabling other profiles until they feel there is a reasonable way to secure BT for other profiles. I find the Jabra headsets (I use the Jabra GT250) and the Plantronics ones work best - there is a rumour the Motorola ones have some 'noise' on the 7250 but I don't know if this is true or not.
5. Battery life is good and the info on the site is accurate, or as least as accurate as you can be considering everyone's differing usage patterns. There are some standard tests for battery life and I am sure the results you see on the website are from the one Verizon supports.
6. Yes, the Vibrate function does seem to me to be very good.
7. Personally I like the holster that comes with the device. Easy usage on a belt - one hand in and out. You will find you take the BlackBerry out a lot, so that is very important.
In your summmary the BlackBerry is going to give you what you need over the Treo however you are going to have to fork out for some kind of data plan whatever decision you make.