I did come through CTC yes.
The smallest I've heard of is just under 650 hours but that included a month and a half of being off sick. I don't think I've known anyone do less than 750 a year.
As for keeping your licence active it depends on which one. The CPL/IR that you leave CTC with only needs a yearly IR renewal to be done - the first of which can be done in the sim to save cost.
Once you're type rated and effectively have the fATPL then you have recency requirements but I can't remember what they are off the top of my head - I wouldn't be concerned though if you're working as you're unlikely to drop under those requirements and the company monitor it anyway.