Paul
First you need to find your 150 mechanic/IA, this should be a 150 knowledgable mechanic or one that can learn from websites like this one, as a last resort a mechanic that will read and follow the maintenance manual will work also.
You need to be comfortable with his style of repair/inspection. Example; stuck exhaust valve. The repairs can range from a cylinder overhaul to my favorite trick of cleaning the valve and guide without removing the cylinder, it depends on your mechanics experience and knowledge level. Same thing goes for the inspections, there should be a list of airworthy( can"t fly till it's fixed) items and this is getting worn we should fix it some time items.
Trouble shooting is another area where a less than stellar mechanic can flush aviation units down the drain quickly. Aviation Units= AU = $1000.
Ideally I recommend you have your mechanic annual the plane you intend to buy so you both are satisfied/aware of it's condition. That almost never happens tho. The 172 I bought is one I have annualled for 8 years, I think I know it's condition pretty well as well as it's short comings, that is a rarity when buying aircraft! Having a disinterested 3rd party look at the aircraft is cheap protection for you.
Sounds like you gave already made the choice of airplane type so we can skip that. 150= fun flying and really fun cross country flying.
Now to find a good airplane for you. What equipment do you want/need? Most 150s are VFR as is 29T, a comm, transponder and encoder, intercom and an old Garmin 100 with a AV8OR on the yoke, worked good for all our flying. Do you need or want more, then make your list and start narrowing down the choices. Same with engine times, paint and interior and any personal quirks like 29" bush tires you may have.
What density altitudes will you be operating from, there may be a reason there are no 150s around you. On hot days you can't load a 150 very heavy and get any kind of take-off/climb performance, it becomes a 1 man airplane.
These are old airframes and as long as the damage/corrosion/ wear has been fixed correctly I don't get too worried about that, same with airframe times, they will last a long time if the maintenance is done correctly. I inspect a 150 with 14000 hours on it, probably tighter than most 150's cause if ianything is loose it gets fixed.
Engines; they will go along time also but they need to be flown regularly, most of us do not fly enough to make that happen. The cylinders on the O-200 are the problem area ie stuck valves. I advocate regular inspections to know your valve condition, just like the 500 hour mag inspections. The aerial photographer I work for flys 8 hours a day, changes oil at 80 hours, no filter, and we got 6000 hours out of the last overhaul, it wore out 3 sets of cylinders but the bottom end looked great. Flying is not hard on them, sitting is.
My $.02 Alan Core

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