Can I use a US G1 in UK as pre-paid or month-to-month contract?

[UStoUK]

In a couple of weeks, I will be moving from the US to the UK for a year. Upon researching cell phone plans, it seems the most cost efficient option is to take an unlocked GSM phone with me and purchase a prepaid-SIM card or use a month-to-month plan. I have always used CDMA providers in the US, so I need to obtain a quad-band GSM phone. I am considering purchasing a used US-version G1 phone and then getting it unlocked.

If I do this,

1. 1: Will I be able to use this unlocked-G1 phone in the UK?
2. 2: Can the unlocked-G1 be used with any cell phone provider or does it have to be T-mobile Europe? (For example, can I use it with Vodafone or O2?)
3. 3: Can I use a prepaid SIM card from another European cell phone provider (such as Vodafone)?
4. 4: Are there any features that won't work if I do this (such as web access, GPS, etc.)?

I appreciate any help you can provide.