Hi Yodi,
About the engine issue, I have the same problem, there are 2 different mutually exclusive situations to consider:
Calendarial: Engine is older than 12 years from new or since last overhaul, regardless of hours remaining.
Total Time: 2'200 hours if I am not mistaken + 10% tolerance
For Aerobatic aircraft it's 1'400 Hours
Whichever comes first puts the engine "On condition" BUT for private use only.
For training purposes within an ATO at least for licence training, debatable for ratings, (Aerobatic, night, towing) the above conditions must be met.
Lycoming issues recommendations only (Don't know abot Continental) for calendarial deadline overhaul, but authorities in Europe makes this mandatory for use within ATO.
We live in a world of potential litigation issues around every corner, this might be one of the reasons for this, the other which is more subjective is corrosion to critical parts, camshaft lobes, bearings and cylinder walls originating from sporadic use.
It is very likely that an abused engine used daily within a school with overrevv's cold starts, failure to warm up properly may reach TBO whereas a carefully maintained privately owned engine flown sporadically may have issues well before that.
But there are means to diagnose health of engine, by oil analysis (To be effective must be done regularly and matched against previous findings), compression tests and visual / scope inspection of vital components.
It is very very unlikely that a privately used a/c will ever reach the TT TBO while on private use, it will reach the calendarial deadline first.