Ditto Lawrence on the purchasing of parts to find a problem. On a ten year old car, it's just as likely to be a corroded connection or frayed wire or dirty component causing you a lot of your problem(s).

Try the free stuff first. Clean the battery terminals. Clean the connections at the other ends of the cables. Clean the ground connections. Clean and assure good connection on all the sensors, Air Mass Meter, etc., etc. Clean the throttle body and Idle Control Motor and wire connections. Check adjustment on throttle position switch. The 700/900 FAQ's on this site have some good pointers.

If you're electrically inclined, jump certain components that you suspect might be a problem.

Get it to start consistantly and then work on the other things. It sounds like you may need a new thermostadt. There again, you can remove it, put it in a pan of water on the stove along the wife's turkey thermometer, and observe at what temp it opens. (It may be open all the time.)

Your car is at the age where it's going to start to test your love for it. Hang in there.