I was looking around the direct gov website and couldn't find answers to these questions?
When I apply for a provisional license, do I have to do anything to prove I have a valid US license? I don't think so, but how they know you're entitled to drive without the L-plates,etc...? Do you just have to have your US license with you when you drive?
Also how long is the provisional license valid for? If I don't get around to taking the driving test for like 13 months, am I ok? Not that I'm planing on taking that long but getting my license isn't going to be a priority.
You don't need to prove you have a valid US licence, and you don't need the L plates to drive as long as you have been here for less than one year and have your US driving licence (some people prefer to put the L plates on, though, just to let people know they are inexperienced driving here - they only cost £2 and you can buy them at most garages.) At the moment, you don't even need your provisional licence to drive, you can just drive. You should indeed carry your US driving licence with you when you drive, and I would think you should bring your passport, too, to show when you arrived to UK so any officers who might stop you could determine your right to drive without a UK licence.
Your provisional licence, I believe, is good for quite a long time. I think someone else on the forum applied for her's 5 years ago and just now completed her driving test. So you should be fine there. However, once you have resided in UK for longer than 12 months, you will then be treated like every other learner driver here, meaning you will have to be accompanied by a driver who is over 21 years old and had a full licence for at least 3 years, display L plates, and not drive on motorways until you pass your driving test.
I think when you are just settling in, it's ok to put getting your licence on the back burner. Just being here and getting adjusted to things can be pretty daunting for some people, so adding the stress of driving tests might only make that adjustment harder. I waited until after I had lived here for one year to get my provisional licence and start my lessons, because I just now feel ready to tackle that. It may be a different situation, though, if you are on your own and must drive to get to work or something like that, in that case I may have pushed to get my licence before the year was up. Good luck with whatever you decide to do!