Hi
Welcome to the madness

Very nice truck. Looks great! I like that all black appearance.
As for every new owner: Get a service- and workshop manual (there is a resources thread on top of the 70s tech foru) and familiarize yourself with parts diagrams and parts resources for your rig (e.g. Partsouq.com, amayama.com, todiy).
The first thing you should do is to baseline the vehicle: Do a (really) complete service and address any obvious issue as needed. Get to a regular service schedule. (Whether a blower fan issue is a 'needed' fix, is up to you

).
Also check on your electric wiring and remove any sketchy rats nests and appliances (Japanese trucks are infamous for 'electrical upgrades' done by POs)
'Upgrades' then pretty much depend on what you want to do with your rig and what probably annoyes you. I personally think, Landcruiser are pretty well engineered rigs, which generally do not 'need" real upgrades.
Most people strive to improve the ride and general offroad abilities with better suspension and tiers. Don't know what your suspension is about, but your 33 tyer size is nice, looks good and is suitable for most offroad activities, I guess.
A factor that annoyes many people are electrical hubs, and many consider switching to manuals. But yours appear to be manual already.
Some people think, most engines need to be DIY reengeneerred in any case

, emissions control remove, turbo improve, EGT control and what. I'm not in this. Others may charm in.
In Japanese trucks, the entertainment- and navigation system might not be suitable for your area, so thats probably a topic to upgrade.
Most people deem cupholders and armrests the most needed upgrades. I agree with that.
Not necessarily an upgrade but rather equipment: If you plan to go offroading, get yourself some basic recovery gear and stow it somwhere suitable. (May end in upgrades like holders for shovel and maxtrax, solid towpoints, winch ..)
Other than that, it's all about outfit for purpose and liking (including look): Camping, cooler, awning, water-supply, towing, roof rack, rims, sound, lighting, navigation, communication, winch, rocksliders, compressor, ... You think what you want to do with it and name it.
For myself: I improved the ride by new suspension and tiers (but mine is a 39 year old, leafesprung BJ73). It already had a winch, too. I added a spade and a fire extinguisher and equipped myself with some recovery straps, winch pulley and a toolset.
I removed the rear seats to make space for camping gear, fitted a simple awning, fitted a foldable table on the rear door, fitted something to sleep in the truck, fitted some electrical outlets in the back and a dual battery solution, fitted some holddowns for stowing boxes and water container.
I also fitted a new radio (rather for technical reasons in my 24V system, speakers where upgraded by PO already) and installed a mounting for my phone or tablet for navigation. That's about it.
Have fun! Cheers Ralf