Is it a good idea to buy clean-ESN phone from eBay to avoid mandatory data plan?

[New Daddy]

I was about to upgrade my XV6700 to TP2 online, but one thing bothered me that made me stop. The $30/month (or $50/month) unlimited data plan that you cannot opt out of (which comes to $720 or $1200 for a two-year contract!).

So, now I'm thinking of buying a stock, unlocked phone from eBay and have it activated. Since these unlocked TP2 range from $300 to $450, I'll still end up saving a few hundred bucks!

Is this a workable idea? Especially,

(1) Will Verizon still make me sign up for an unlimited data plan anyway if my new phone purchased from a third-party is a PDA phone?
(2) When I shop on eBay, do I still have to purchase verizon TP2 or can I buy AT&T, Sprint or T-Mobile versions of TP2 without having to worry about activating them? Will there be any problem with future updates from HTC, if I do not buy a Verizon TP2?
(3) Is an unlimited data plan a necessity? I never needed unlimited data plan with my XV6700, because I'm almost always located where WiFi is available. For the few occasions that I need 3G data network, pay-as-you-go was cheap and sufficient. Is there any reason to believe the situation will change with Touch Pro2?
(4) Any other foreseeable problem in this scheme?

Thanks~