With ur commute...the z650 will be a better choice...itll cruise easier on the highway so u will feel less stressed n less fatigued... actually a versys650 will be even better...same engine as the z650...but with a more relaxed riding position n better wind protection.

As mentioned, engine is robust so the normal service costs depends on the engine oil u use...oil filter typically around rm50.

Also get long lasting tires..like sport touring tires.... not sure about the prices for z650 size...

Valve clearance every 40k must be done... don't listen to those who say dont need to do....its called "preventive maintenance" for a reason.... Meaning u do it to avoid unwanted things happening....if u only do it after something happened...thats not maintenance, thats better called "repair"

Next up is chain n sprocket...no idea how much but im assuming around rm600? Proper chain maintenance n lubing can help prolong. And again with ur commute..id highly recommend a scottoiler.

as a fellow naked bike rider, i can confirm that a taller windscreen will help. as long as u can get the wind directed above ur chest, u wont get pushed back as much.

Also, choice of helmet matters as well. some helmets cuts through the air better than others. this will help reduce neck fatigue on longer riders.