The dealer should tell you that you can get the valves checked very safely between 600 and 1000 miles. You don't need to get it there at 600 on the nose, and no, this will not void any warranty.
An oil change can be done easily if you're even somewhat mechanically inclined. It will cost you well under $20 using Honda conventional motorcycle oil. Even if you're not great with a wrench, you can still learn this skill and save yourself some money. You'll also have peace of mind knowing it was done exactly right. I also think it's quite important for every rider to know his/her bike well enough to at least perform all basic maintenance.
DIY Oil Change
Same thing goes for the chain tension check, you should be doing this regularly anyway and it's not difficult. It's a 2 minute check and 10 minute adjustment, but you'll need the right tools (including a torque wrench).
Ask what they would charge for just
the valve check & adjustment, minus the oil change & tension check.
FWIW, my dealer charges around $170 for the first service - valve check, oil & filter change, chain tension adjustment.
All that said, if you're not comfortable with any of the above, of course have your mechanic do the work, and/or teach you how to do it (the decent ones have no problem with this).