Remember its all timed so if you stop now and start up in two weeks you will finish at least two weeks later. There are some treatments that can be done during and after that are covered by your Dr and invisalign that if you put off your treatment too long you will sometimes it will cost you...
Unless the sport requires a mouthguard it should be fine to wear your aligners. They hold so well to the teeth that they are unlikely to come out if you fall or get bopped in the head. But if your sport requires a mouthguard (football, wrestling, basketball) than just remove you...
When it comes to Invisalign trays, typically the higher number would be the last set. So if you have a higher number than odds are that is where you left off.