How often do you have to service your Studer or Otari deck ? Home not pro environment.

Should have said:
"Other than cleaning the heads and setting tape bias for the different tapes"

I have a Crown CX-822 reel to reel. I bought my unit from Chuck Ziska, Crown engineer that now refurbishes them. I haven't had to service it yet. BTW, I am not sure there is anything to service other than cleaning the heads. 
To answer your question, tapeheads.net is a great resource. There is a very well respected technition in Los Angeles that works on Studers. I don't want to post all his info on a public forum, but if you PM me I can give it to you. Or you can get an account there and quickly you will see who it is. Once again I never used him, since I have a Crown, but I read his posts and others seem to be very happy with his work. 
BTW, I really like the ATR MDS-36 tape. I just bought one sample and evaluated my recorded frequency response on 7 1/2 IPS (my go to speed) and I thought for my deck it was better than the Pyral. YMMV.
Typically, as far as I understand, and reading through the Crown maintenence manual, other than cleaning the heads there is not much to do , for the amount I actually play the unit. That's if your unit is in prime shape when you acquired it.

I only use new tapes. These are the 3 tapes I use. 
RMGI/PYRAL LPR-35 (1mil tape)
RMGI/PYRAL SM-911
ATR MDS-35 (1 mil tape)

I have one sample of the MDS-35,  but I really like it, frequencies record very well on that tape from my Crown CX-822.

For those curious, there are 1/2 track and 1/4 track. All 1/4" tape.   So 1/2 track means that 2 channel stereo is all on the tape, then entire 1/4". So approx 1/8" for left channel, approx 1/8" for right channel. This is what is used for master recordings. The majority of consumer units were 1/4 track. So each stereo channel, right is approx 1/16" and left is approx 1/16", so stereo takes up half the tape. That is why you can turn the tape over and record on the other side. Just like cassette. Since the magnetic flux density is not as high as 1/2 track, 1/2 track is always used for the highest fidelity master tapes. Sometime people also call 1/2 track, 2 track and 1/4 track 4 track. In fact the commercial tapes produced back in the day actually had a 4 on them for 4 track.

So before you buy consider the following:
1. 1/2 track or 1/4 track?
2. Tape speed options? I like 7.5 IPS and 15 IPS 1/2 track.
3. Get a deck that is actually servicable. Some Japanese decks noone will service, there are no parts available. Typically Studer, Revox, Crown are servicable, there are others as well.
4. I use my deck for recording my album's and playing them back for longer play while not critically listening. Since I get 1 hour 36 minutes from 1 mil tape.
5. I wanted the best sounding deck, I can A/B the album and tape during recording since my deck has read after record and I am hard pressed to tell which one is which. Hence 1/2 track 7.5 IPS.
6. Tape heads.net is a great resource.