The problem with a full service is you don't know exactly what they changed, even if it might be written down. The bike is new to you and you will have things to learn when you start riding it. The coolant mix spec. is either BMW pre-mix or 50% undiluted Glycol with inhibitor and 50% water. You don't say what temperatures your garage will get down to?
+1 on coolant should be 50/50. Almost any anti-freeze is sold that way, although 100% can be found. 50/50 works much better than 100% - see the table on (most) jugs. Also, yes, it's helpful to know where you are to figure out reasonable low temps. If the garage is attached to the house, it's going to be warmer (relative term) than a detached garage.
I think I would suck out some coolant from the reservoir under the seat with a turkey baster (easy to get to) and put it in your freezer. That should take it down to about -18 deg C. If it doesn't freeze you know you are good for that temperature.
Better still, use an anti-freeze tester (see your FLAPS - Friendly Local Auto Parts Store).
If you still have doubts storing during Winter you can remove the right plastic, slacken the water pump hose and drain the coolant completely. But disconnect and remove the battery for trickle charging and tie a BIG label on the battery leads to remind you to refill the coolant!
Draining and changing can't hurt (if done right - see your Clymer service manual - you have one, right?). You'll know for sure what's in there. Don't forget to run the motor afterwards to make sure the new stuff is everywhere. Also, gas stabilizer is a good idea. Remember that it's going to take a short ride to get it into all of the fuel system - dump it and forget it isn't a good choice.
You can pull the battery or invest in a Battery Tender brand trickle charger. It's helpful if you leave the bike idle for extended periods, too. They include an external connector as well as the usual clip leads. The connector means the saddle doesn't have to come off to charge the battery. A fully charged battery will withstand very low temperatures without a problem. Partially discharged - not so much.