You are probably looking at a shade over 3 hours - close enough that you might decide to have a crack at sub 3 - though the risk is you end up blowing up and getting a slower time than you otherwise might.
Weights tend to divide people as to whether they are useful or not - personally irrespective of whether I thought they can help some distance runners - I wouldn't add weights into the programme if you've never done them before. Additional risk of injury as they are new to you and as you'll be upping your mileage adding weights too might be too much of an increase in training load in too short a space of time.
When I did London I stayed at my brother's place in Bermondsey - it was no hassle getting across London on the tube so if you can't get somewhere close to the start just get somewhere a convenient tube ride away.
The biggest mistake I made training for marathons was peaking too early - thinking I'll keep adding more to get a faster time and then getting injured a few weeks out and not making the start line. Usual stuff - never try and catch up on missed sessions, be conservative with niggles and all that - you've got to be on the start line to be in with a chance of a decent finishing time.