update: after 5 years of storage, i connected a battery, put some gas in it, and she fired up like she last ran yesterday.
i ran it for 15 mins, and did an oil change with fresh oil, then I ran the bike for another 5 mins to get the engine coated in the new oil, and waited for it to die from lack of gas. also added a bit of fuel stabilizer just incase some fuel remains in the injectors even after running it empty.
i checked the coolant overflow, there was 5 metric tons of limescale in it, as I always say, better to do the work yourself! my father brought this bike since 87' to BMW for servicing, and they put water from the tap instead of distilled water, unbelievable. i cleaned the overflow with vinegar to get all the limescale off.
eventually, when I'll bring this bike back to life I'll do some deep cleaning because the coolant tunnels are probably full of gunk and limescale.
as for changing coolant, gear oil, and brake oil - too much work ain't got the time, especially for a bike I'm not gonna use, as other have stated it's already been like this for 5 years so potentially if something had to go wrong it probably already did.
main reason I changed the oil is that I was told it turns acidic from carbon deposits and combustion and it can damage some o-rings and such, so I put some fresh cheap semi-synthetic oil in it.