Not sure about the price to service it but it's pretty easy to do it yourself + you get to learn more about your bike.
Plugs are easy, air filter should be a case of clean, dry, re-oil. Not sure if this model has a fuel filter but again if it does it's easy to replace. Change the oil is pretty easy. I'd suggest investing in a workshop manual which will show the basics for servicing. Again, not sure about the 600 but valve clearances should be checked and adjusted as well.
Would be a good time to check the battery levels and state of charge. Check the fluid level in the overflow tank for coolant. Check the radiator for actual coolant and not just water - actually wouldn't be hard to flush it out and replace with new coolant.
Plugs, oil / fuel filters, oil. coolant.
Just check to see if that "full service" includes valve clearances being checked too.
For helmets it's worth trying on as many as possible - some will fit better than others and the range in prices will be much better. Same with gloves.
That's just my $0.02 tho - lots of more experienced people here with advice
