Advice needed about changing fluids on a truck with extremely low miles.

I bought a garage-kept 2017 SR5 V6 4X4 Tacoma with extremely low miles from my dad. It has a dealer installed lift kit and bigger tires, and he found it hard to get in and out with two hip replacements, so he always drove his smaller truck. It only has 12K miles on it. He has had the oil changed at the Toyota dealership every year and driven it a few miles in 4WD every month as suggested in the manual. He purchased an extended warranty that doesn't expire until next spring, but hopefully it won't ever be used.

I have a good shade tree mechanic. He replaced all the fluids in a Subaru Outback I recently picked up as my wife's daily driver for a fair price. My question is... What all do I need to get changed in the Tacoma. Since it's a 2017 model, that means it was on the lot in 2016, so it's about 9 years old.

Here are the services I'm pretty sure it needs just due to the age of the fluids.

1. Transmission Fluid

2. Differential Fluid

3. Transfer Case Fluid

4. Coolant

5. Brake Fluid

Here are services I'm not sure it needs with only 12K miles and having been kept in the garage. I doubt it has ever spent a night outside.

1. Serpentine Belt?

2. Spark Plugs?

What do you think? Is there anything else I need to worry about?

With the larger Nitto Trail Grappler tires (also installed as a dealer package), I felt it was a little sluggish, so I got an OTT tune. That made a big difference. I also changed out the grill, blacked out the badges, and got rid of the chrome bumper caps. I just went with generic black ones. I'm hoping this truck will last me a long time if I keep up the maintenance.