Can only guess as there is a lot of change at the moment but they are reasonable guesses.
Summer roster B757 at Luton is likely to be nearly all day/night flights for new joiners. Very likely to be at least one based 757 there, mainly on the schedules. All senior LTN 757 FO's are going either on the 767 as a FO or getting a command on the 757. 767 will only have a limited number of crews for the forseeable future. Any FOs going on the 767 have been in the company at least 5 years. Hopefully all 757 crews will be checked on the 767 at some stage but likely to be at least 12 months before this happens.
If you are new to the company then a LTN FO will do most of his work out of Luton during the summer - more likely to get trips away in the winter, ie Dublin, Bahrain. Odd trips in summer would be to cover LGW/MAN.
Layover time? Min rest to 16 days!
Most LTN 757 crews have been averaging 400-500 hours per annum for the last few years. LGW crews do about 650.
767 has not arrived yet. Call back in a couple of months.
Monarch have a strange basing policy - still haven't got it right. Some would say it is a very expensive way of doing things.
Hope this helps. All the best.