Change the oil and filter and take the car for a half hour run or so, then put on stands with the handbrake off.
Tyres should not bear the weight of a car on one position for too long (even when pumped up hard).
Open the fresh air vents on the facia, put in a desicant, if you can check out mobile home/caravan suppliers as the moisture traps they use do not need attention for at least three months. You say you are getting some work done on the car then opening the windows for a short while will always help.
If you can cover the grass that will help, don't bother with a car cover as you would need a very expensive one to avoid the condensation caused by cheap ones.
You are better off NOT starting the engine every so often, unless the engine gets right up to running temp (not just the temp gauge) then the engine will just end up with a shedload of condensation which will 'mix' with the oil causing sludge.
The diesel in the tank can go a bit mingy after a few months so consider draining the tank or at least keep it low then fill up with fresh and change the fuel filter when returning the car to use, do not forget the sedimenter if fitted.
Disconnect battery and if possible place in dry place (not on cold garage floor), if trickle charge is available use it, not an issue if the battery is new.
Could the weather in your area change for the worse in the coming months i.e. freezing temps? If so check antifreeze strength.
Other than that as already mentioned three months is not a long time.
Hope that helps
regards
Dave