I do not think you will have much of a problem. 4-5 hours is plenty of time. I have done this numerous times and only once did I have to run for it to make the connection.

If Virgin has an interline agreement with American, you should be able to check bags all the way through--just show both sets of tickets when you check in with AA.

Most agents will understand if you miss a flight due to problems with a previous flight. You may have to go stand-by and if there is no more room that day, you would need to pay for all of your meals and hotels but other than that go for it.