Hi,
DIY oilchanges are no problem.
imo you always change the filter and the copper seal ring under the carterplug.
It does not cost much extra.
6000km : check your brakes.
I know...@ almost 12000km one of the front brakepads jammed and the other side is almost gone.....waste of 3 good brakepads.....
Caused by roadsalt and roadmuck this winter, we've had a lot of that this year...
Take the brakes apart, and use some coppergrease (Suzuki does not use any) to mount them back again. front & rear
Wish I did that @ 6000km, now I know better, costs are 40 euro to order 4 brakepads (Ebay)
Check the chain, chain slack and allignment of the rear wheel.
Check all lights, check tires (pressure and look for nails...)
With 12000km I changed brake oil and the darker clutch oil (DOT4)
Make a note in your service manual with the date and the worke done.
very important for warrenty and later (much later) when you sell your bike.

Have fun !
DIY is the best way to learn everything about your bike.