Going to start doing my own oil changes. What's the best brand oil to use? I have a Suzuki, Yamaha and Honda motorbike. Same for all or different?

√ owners' manual.

Are all the bikes the same? Ie all CVT or all manual gearbox?

Castrol Power 1 is about as good as it gets..Works well in all Thai made bikes

if you dont shy for cost and got some high performance machine then motul 300v is the way to go