Hey bud, let me be the first to welcome you to the world of Toyota
I just bought a '90 T4R a few months back myself. It also needs a good tune up, but I have been able to do some of the simpler things on my own.
A few things to start with that should be relatively cheap and easy.
==> Chilton Manual
It doesnt cost much, and contains pages upon pages of detailed information about how to do just about anything to your truck. A MUST if you don't at least have your owners manual. Find one for your truck at most parts stores.
==> Sea Foam!!!
This stuff works wonders and is a lot of fun, too! One $6.00 can of this stuff will safely and effectively decarbonize your intake manifold and combustion chamber, clean fuel lines and injectors, and clean your engines oil lines while freeing up gunky rings and passages.
Grab a can of SeaFoam Motor Cleaner, and park your rig somewhere with plenty of ventilation. Depending on your particular engine, find a vacuum or brake assist line that evenly feeds into your intake manifold. Have a buddy crank the warmed engine back up and hold the RPMs @ 2,500+ while you slowly pour 1/3 of the can into the tube. Your engine will start to stall as it sucks the Sea Foam into the combustion chambers. If it stalls before you get it all in there, crank it back up and keep going. Once you get it all in, shut off the engine if it's still running and pour just a little more into the line. Now you need to let it sit while you do the next step.
Take another 1/3 of the can and pour it right into your crankcase. Just untwist the cap where you fill your engine with oil, and dump it in there. The Sea Foam will flow with your oil to critical engine surfaces, removing carbon deposits and cleaning narrow passageways. **Be sure to get an oil change within the next 100 miles or so in order to drain out all the impurities and carbon that the Sea Foam has removed from inner surfaces. If you aren't ready for an oil change quite yet, then skip this part and do it later when you are.
The last 1/3 of your can should go directly into your fuel tank. It will stabilize your gas, clean fuel lines and injectors, and removes moisture.
After the Sea Foam has been allowed to sit in your engine for about 15-30mins, it's time for the show! Crank it back up and hold the RPM around 3,000 RPM. You'll notice a huge plume of thick white smoke blasting out of your tail pipe. That's all the carbon that used to be in your enigne! The smoke should thin out after a few minutes and then you should drive it about 15-20 miles (in a rather spirited, high RPMs fashion
) to get the rest of the crud out.
==> Oil Change w/ Synthetics
This might stir up a debate, but in my personal experiences synthetics are the way to go. They run a bit lighter and flow easily through your engines tight spots and lubricate metal surfaces better than conventional oils. Synthetics also tend to contain more/better additives that clean and protect your engine from stress and contaminants. And if frugality is your primary concern, then consider that synthetics can go much longer between oil changes than conventionals.
==> Spark Plugs & Spark Wires
It's what makes the magic happen! Dirty or worn spark plugs will rob you of power and fuel efficiency. Throw some new plugs in there! A lot of Toyota guys refuse to put anything but NGKs in their Yotas, but I just put in some E3 Diamond Fires... and so far they do seem to help with gas mileage a tad.
In any event, yanking the old plugs out will give you a chance to inspect their condition. This should give you some insight to the health of your engines insides.
==> Clean or Replace Air Filter
A dirty or blocked air filter will cause your engine to eat more gas than it should. Inspect yours to make sure its clean and air can pass freely through it. You may decide to replace it with a lifetime high-flow filter like those offered by K&N. You can get them at most any parts store and cand add a small percentage of horsepower to your rig!
==> Inspect/Replace PCV Valve
The PCV valve recycles unburned fuel vapors from the exhaust manifold back into the intake manifold. A clogged or dirty one might cause an engine to run rough at idle or poor gas mileage. Inspect yours to see if it is clogged. Replacement is cheap at about $5.00 and takes only a minute to install.
==> Inspect/Replace Fuel Filter
This little guy filters gas on it's way to the engine. An old dirty filter can cause poor fuel flow resulting in lost power and possibly stalling. Replacements are relatively cheap in the $15-20 dollar range. You'll find your current filter installed somewhere under the car - check your manual. Also take care when removing the fuel lines from the current filter. Your gas is under high pressure in those lines and will spray out if you don't follow your manuals instructions precisely.
==> O2 Sensor
Think about replacing this, too, if you aren't passing emissions or if you're rig is older. Your on-board computer uses this sensor to know how to properly mix the air and fuel in your engine. A new one is gonna cost you around $80-100 bucks, but they are pretty simple to install.
==> Belts
Replace 'em. Cheap. Easy. Just a good thing to do.
==> Timing
Get a timing light and set your engine timing. It's pretty easy to do, and the lights aren't too expensive. But making sure your timing is set right will ensure your spark plugs are firing at the most efficient time.
==> Use the Right Octane Gas
On some of these trucks, Toyota recommends an octane rating of at least 90. Different octane gas burns at different speeds, and if your engine is designed for a higher octane rating, then running lower octane fuel may cause it to ping or run rough. I know gas is expensive, but be aware that your rig will run better with the right fuel.
Can't think of anything else right now. And this is all simple stuff, really. I have done most of the above and still have other problems to work on. Best of luck with your projects!
So I won't be any good at helping you with yours. I have seen a ton of other threads here on the subject, though. Seems the rear window is a common problem for these old rigs.