where do we start my friend?
check and read all the service records you mentioned. I personally have an Excel sheet with all my maintenance items derived from service records (Paperless approach, and easy to analyze all the data).
timing belt and water pump if they haven't been done (search the forum on this point, if you need to do them there are various other things you can replace along with them at the same time)
either a new radiator or an external transmission cooler with bypassing the stock cooler (the former is easier IMO) - read about the pink milkshake.
fluids - what mileage were they last replaced? if you don't know... doing them will give you a fresh place to start logging it.
list of fluids besides the oil change - coolant, transmission, power steering, brake, front and rear differential, transfer case fluids.
spark plug wires and spark plugs
air filter
fuel filter
pcv valve and grommet
lower ball joints at your mileage if they have play.
unfortunately, this isn't even the complete list. if you can get past all that, check the undercarriage for other stuff (tie rods with leaking boots, cv boots, pinion seal leaks on the differential, brake pads, bad steering rack bushings, etc etc). A tip for you -- Firestone auto care will check all of this for you for free, just tell them you need a 'brake check'.
take care of the 4runner and you will go further than another 50k miles, and always reach out for help -- this forum is an incredible place.
