My headlights will only work in the "bright" position. A mechanic suggested that I replace the "multi-function switch", but Chilton's doesn't mention, specifically, a "multi-function switch".
Both the driver's and passenger's seat (butt only), as well as the center arm rest, have serious cracks. Is it advisable to buy a seat cover from Pep Boys even though the covers are not tailored for adjustable head rests, or look through junkyards for replacement seats?
When I turn the ignition switch, most of the time, there will be a single click noise (not as if the car was trying to turnover) and then nothing. After many turns, the car will eventually start and idle normally. On hot days, it is much more likely the car will start immediately, as well as if I've just turned the car off after a long drive. Any advisable diagnostic tests to determine what I need to do?
Any help much appreciated.

Your ignition problem is clearly a "starter" problem. This is a classic symptom of a starter that has a dead spot. If you are handy, the starter is "re-build-able". It's about $40 for a rebuild kit....go see the toyota dealer.

Else, you will have to buy a new starter (after market...try that first if you can't rebuild it). The rebuild is easy, there's usually a worn angle bracket that your shaft runs on. Once you have it apart you will laugh at how obvious it all is. The risk is that you "maybe" can't figure it out...and then you'll have to buy a new starter. Big deal ! So you spent an extra $40 but look at the experience you gained.

1)Headlights only works in high beam only? How about low beam? If they don't work in low beam, you might have to replace the 2 bulbs. Very simple to replace if that is the case.
2) Seats worn out? I suggest leave it the way it is or you can purchase a seat cover to save some money rather than going to a junkyard ect.
3) When you try to start the car, sometimes it goes click ect., it is either the starter selenoid might be bad or the whole starter is bad. To test it, at night, turn on your headlights and try to start the car. If it goes click and the light remained bright, your batter is still good and if the lights dimmed, your batterry might be low so the starter can not start. If that is the case, charge your battery and see if there is any improvement. If not, replace the battery.
4) If the battery is good, check the starter electrical terminal to see if they are loose. Make sure it is tight. To test, I suggest you turn on your igntion and leave the key on to ACC and use a screw driver to test the 2 connections at the starter. Be careful because you might see some sparks coming out. Kind of scary but it could be done. If the starter is good, it should crank the engine.
To make the story short, it is either the starter or the battery. Have it check out and replace any if needed. In my honest opinion, I think you should take the starter out and take it to Autozone and have them check it out for you, free of charge. Hope this help.