Hiya
Do take a look around at the various threads about Americans coming here and then doing the driving thing. Each one of your questions has been covered extensively before!
Not being a deliberate downer, but with the current economic hole the UK is in, costs for car's and driving as well as public transport are only going one way - Up.
Insurance prices have significantly increased over the last 6 months or so, quite a few of the car related forums I'm on and plenty of people are getting shocks this year when their renewals are coming in. My own policy went up £250 with no change from the previous year for instance. It will depend on your postcode as to what level of ludicrous insurance quote you'll get, but factor this known increased cost that's happening all over and to everyone really.
related, the cost of our already very high priced fuel is also going up, again factor that into the kinds of car's you'll be wanting and realistically going to be able to afford to run.
Public transport isn't really immune either, fares will most likely rise - they also have to pay for higher fuel prices even though I think they get quite a discount compared to consumers at forecourt's pricing.
You'll need to factor in all of this for when you choose an area to settle in here, but it sounds like you've already chosen and know some of the links into London ? where is that by the way?!
Taxis - extremely expensive and a pure last resort measure for me. For the 8 or so miles from Heathrow to my house in Slough, I had to pay £45 for a black cab, I was so knackered after flying in, I gave in very reluctantly. I later found out a private mini cab place would've wanted £28 which is still to me, extremely expensive.
Insurance brokers are pretty much in every major town etc, a quick lookup on the internet as well as local newpapers and a stroll down the high street will usually find you a selection!
Hope this helps!
Cheers, DtM! West London & Slough UK!