I agree with justinm,
We had a tech that had 250-300 units and could handle the work load. He was and older guy that loved to get in there and get it done. Loved a challenge.
Keep in mind ,they all don't break at the same time and if you have regular P.M schedule it helps.
There are day's when i have to pick up the phone to make sure it is still working, it's so slow.........the next day............30- 50 calls. The joy of the lift truck industry