What I find is that old machines sometimes don't boot from the recovery media. The reasons why are well known (old drive, lens cleaning, or the need to duplicate that CD) so while all this is known, why not plow ahead and try?

Overheating is well known. While there were a few models that no cure was ever given (mostly those bad old Pentium 4 models) you can clean the vents, heat sinks and apply new heat sink compound to alleviate heat issues. All this is widely discussed so I'll stop here.