Hi Matty,
Just some approximate info for starters:
1. One CC member required for every 50 seats on the a/c, so assuming a typical 737 loco, either 3 or 4 CC depending on whether a 300/700 or 400/800 model.
2. Most loco operations seem to run with approximately 5 crews per a/c, which is fairly typical for short haul generally.
3. Again, loco ops tend to have the following personnel tied in with the ground handling; 1 dispatcher, preferably load control capable; 3 baggage handlers/ramp agents for loading, ground servicing and pushback duties; 2 pax handling agents for boarding. Realistic turnaround times for domestic ops 20 mins, 25 for international and 35 where a crew change is required.
4. Food and duty free normally only loaded whilst the a/c is night stopped, and not topped up during turnarounds with the exception of milk and dry stores like tea/coffee/stirrers etc. When it's gone, it's gone. Not sure of the costs.
Additionally, don't neglect to factor in the other costs involved such as check-in (usually contracted out too), cleaning (usually a cabin tidy on turnaround and a more thorough clean on the night stop, although some loco ops have the CC do all the cleaning except night stoppers), fuel (might be cheaper to tanker it from home), engineering (some ops only have an engineering agreement in force at home bases) and airport handling charges.
It is also possible that a/c can be utilised in the freighter role during the night (like Jet2 and the QC versions of their 737 300). This tends to be very financially lucrative, but there are also very heavy cost penalties incurred for delays, and continual ops will limit engineering down time and increase the risk of en-route delays.
Best of luck.