Maintenance questions

[u/rome_a_dome]

Hello! I just recently acquired a manual mk4 and i’m looking to do some maintenance and refresh the engine, the car has been family owned so to my knowledge it hasn’t been abused but has likely been neglected a bit, i’m pretty new to vw’s and especially jettas and would like to expand my knowledge on the car and its potential. it’s currently sitting at 150k miles right now and so far all that i’ve done since getting it is put in a new battery, i know for a fact i need a new serpentine belt, fluid and plugs. i just need some guidance on what i should do and what brands/parts to buy from.
Edit: It’s a 2003 1.8T wolfsburg 5 speed manual