Toyota dealership would be the most convenient, as they will have the exact parts you need. No guesswork there, assuming the service person looked up the correct part number (hence why most places are asking for the vehicle VIN number when you order parts).
Toyota ATF runs about $5 a quart, where I'm at. Pan gasket and crush washer usually sets me back about $20, filter they might have to order, as they generally will just clean and reuse the original one (assuming it is in good shape and be cleaned, it will be pretty obvious if it cannot be reused).
To clean the pan, paper towels and some solvent (brake system cleaner works pretty well - inexpensive and no residue leftover). Pour most of the oil out, a few paper towels to get the rest of the old oil and whatever chunks are on the bottom of the pan (note - normal to have some very fine metal shavings stuck to the magnets and the bottom of the pan, but bigger chunks are a problem). Spray down with some solvent, left it air dry or wipe down with a lint free cloth (doesn't have to be clean room spotless, just don't leave big bits of material in there.)
Good idea to do a drain and refill every 30K miles - as you only will be able to drain about 1/4 to a 1/3 of the total system's capacity. Most of the oil is inside the torque converter and the rest of the transaxle. Every 30K miles is often enough that you can ensure some fresh fluid gets introduced in the transaxle. I like to do a pan drop every other drain and refill, to clean up the bottom of the pan and verify the conditions inside. Replacing the filter every 60K miles is fine, I generally clean it at least once. You'll understand once you see it. More of a metal screen strainer, than a filter. Designed to keep large chunks of debris from getting pulled into the pump. Even with occasional towing that I do from time to time - this is a pretty conservative schedule.
