Can't really go wrong with a 562xp I got mine in 2012 and it was retired about a year ago, due to lack of parts availability. I ended up getting a ms400cm.(all I could get at the time, i woupd have bought another 562xp) Up untill that point the 562xp was an outstanding saw. Light and very powerful.
It is 100% not worth rebuilding. I did rebuild one (a 2016 model) it was cheaper to buy a new complete crankcase then new bearings, let alone all the special tools needed to split the case. Just that and a top end and you'll be 3/4 the cost of a new saw not counting gaskets, carb kit (if they are even still available) any intake, fuel line and your time.
I found a 20" to be well suited I hard wood, with occasional 24" use. Give it a few tanks to really come in its own. Muff mod woke it up pretty decently. I did my own. Can't remember the size of pipe I used, was a good improvement, but didn't make it near as loud as the straight shots and wcs bark box on the newer stihl saws.