I own a Krasnogorsk K-3 and I get a new own many years ago, but I did not used it since more then ten years, because I use now "better" ones. But it is really a good camera to start with 16mm. I also used two other ones from friends. So I think I have a "bit" experience with Krasnogorsk K-3. Normally they are nearly unbreakable! So why do you want to have a service without testing it before? You have to ask yourself if a service worth the money of the camera? And if someone is familiar with a Krasnogorsk or if you have questions someone of this forum can help you. Maybe you need a bit Gate Lube, but the rest depends on the camera.
They are sometimes tricky to handle. Some of them are not function very well at some speeds, mostly the seadiness of some highspeed rates are not so good. It depends. With my own one everything is perfect for such a camera. And with all the three I used I never had a problem with a light leak of the foot counter. I read that very often, but I never had a light leak, also with 500T stock. But I always taped the cover, but not the foot counter.
One thing is very tricky: the spring mechanism. It could be that when you wind it up, that the shutter and the transport is asynchron. A very well known problem of this camera model. But it is easy to handle it. When you are finished with your wind up, you have to turn the button to left and right till it the shutter is in the right position. You can see this if you have put the optic away. But you also can hear it with some experience.
By the way you can buy also some cheap M42 optics.
And I would always use a changing bag or tent. And do not use the "film cutter" inside for cutting the beginning. This stupid things are also in other cameras like Bolex, but this is always a danger to have a little bit of material inside the camera, which could make scratches in the material.
And as Samuel said: do not trust the internal light meter.
If you want to buy one second hand, I would recommand a Sekonic L-398 A Studio Deluxe II or III. The model II you get sometimes very cheap second hand and you can adjust it.
I also do not understand what you mean with loop.
I hope you have a manuel. That it makes sometimes more easy.
I also would not use the plastic spools you get with the camera, use metal ones.
With the other things the colleagues near your place like Samuel can help you. I can only recommand companies in Germany and Europe.
You have now a nice tool to start 16mm. I also used it in former days as a second unit camera or for stop motion.
Try it and have fun!
By the way, for fun I also use sometimes Super8 and I develope the stock my my own.