Since you're going the PHP route, you should have a look at http://phpfog.com for hosting. They offer 6 months free hosting. You'll also get exposure to source control via Git and scaling which they assist you with.
Yes, but it only took a day or two for me to get an invite to the Beta after signing up. And I think if you sign up and refer 2 people you get in immediately (although they might have removed this by now).
No, you are just limited to one app and instance at a time. But this should be more than enough to host your average website that gets a couple thousand hits a week.
From the FAQ (not sure if you can access it without being logged in though):
"Will you offer a free version of hosting?
Yes. You get one free application with one instance for 6 months. If you have one app that is using the free instance, you can delete it and you'll be able to create another free one to replace it."