From someone who's done a few XR rebuilds, I recommend the following:
A new timing chain. They're 100 bucks, but it'll keep the top end tight for a long time to come.
New valves and springs, preferably stainless valves. Also have the seats recut. Your valves may clean up ok and be ok for a while, but they wear out. They will start creeping up into the head and you'll need a valve job. It's much better to get them freshened up now and be able to trust that engine for a long time to come.
Countershaft? That front sprocket play does not look good. As said, look at the splines for damage. If you find wear, you need a new shaft. Splitting the cases is required for that. Luckily, it's not that bad at all. I even made videos on it.
Good luck with the rebuild. With new valves, timing chain, piston and rings - that bike will be like brand new.