any year xr 70/80/100 wheels are compatible. I have a set in each size for my 100. The 12/14 set up is great for indoor/short tight tracks and the smaller rear really throws a roost, the 14/16 is really good except no one makes a good front tire in a 16" so if you can get your hands on a 17" front wheel from an older cr80, that is the best set up. The stock 16/19 is ok for offroad/trails but for a playbike on the track I prefer the 14" rear and 17" front.
19/16 seemed to be crappy for any type of riding. 17/17 on fairly narrow slicks was so much fun, the bike felt very stable and really rode well. 17/16 would probably be the best for trail riding. 16/16 was awesome for trails, street, and about anything in between, the bike felt less like a chopper and was much easier to ride. anything smaller than 16's I would buy an xr80 swing arm. 16/14 is nice for tighter dirt pit bike tracks, but for trail riding it brings the bike too close to the ground. I never tried 14/14 but I would think it probably rides just as well as 16/14 in tight dirt tracks and would make a great size for street as well. 12/12 Is the way to go for tight street tracks, but I would make sure to go with a 2.50" rim front and rear.
The next XR100 I buy I will run either 14/14 or 12/12 on an XR80 swing arm. 16/16 would have been more fun with a big bore kit and some narrower tires.
You can slide the forks up a ton, even more with an aftermarket triple clamp. Search my name on here or tt and you will find pix of my bike on 19/16, 17/17, and 16/16. The thread is something like XR100 Mini Stuntard.