First Choice Airways no longer exists(neither does Thomsonfly before i'm shot down) however I will answer your question about Thomson Airways.
Which base?
LGW, MAN are the main bases for long haul with BHX also having quite a few trips. GLA,EMA,NCL and BRS all do long haul but only limited destinations and quiet a few go via another base and you won't operate it.
If you are checked out on the 767 then you can have anything from 0-36 trips.
These are the two extremes with the Thomson Airways rostering system the former is very possible and happens to a lot of crew even at the bigger bases such as LGW or MAN 36 would be assuming consecutive one night trips with no short haul all summer- very very unlikely.
No one can say an average for this comming summer, as there is going to be less long haul than what First Choice Airways used to operate and more than what Thomsonfly used to operate. There is no minimum or maximum set by the company and you can always swap trips if you prefer them or hate them.