Does the oil you purchased meet Nissan’s specs? If so, it is 100% fine to use.

Plan on getting timing belt done, transmission fluid, radiator fluid flush

Transmission fluid doesn’t really go bad with age. If it looks good and doesn’t smell burnt best to just leave it alone until you hit Toyota’s criteria for replacement.

You do need to flush the brake fluid. It absorbs water.

Other than that, I’d suggest you inspect all the rubber hoses and bushings and only replace if they’re showing signs of degradation. Toyota typically used very high quality materials when building these, so it wouldn’t surprise me if they all check out OK. I would not pre-emptively replace any of these rubber components unless you’re willing to pay up for OEM parts.

Your battery install looks fine. Need some diagnostic info:

1. What voltage are you reading at the battery terminals with the engine running?
2. What voltage are you reading at the battery terminals with the engine running, the high-beams on, the rear defroster on, and the A/C running full blast?