Good idea in a general way - I would like to see the pax limit per aircraft rating for each base size though so I can plan my fleet growth.
If the initial Base Size has a Quality Option then the cost increases and also adds a bit of a boost to your airline rating too (factored by passengers flown and base size?).
Also an with the option to select it later too, but taking a hit on the passenger attraction factor during the build as they prefer not to use an airline in a building site as their preferred choice.
Real World airlines only get to rent a part of the airports facility, at Southampton EGHI there are very few airline specific features, it's covered by a surcharge per flight per pax I assume. To set up there I'd need to rent office space (nearby maybe), outsource maintenance to the existing multi-discipline hanger facilities, and a couple of ticket desks. Little capital outlay but not the cheapest way over a ten year period - that's where I'd have to pay the airport to:-
1. build a maintenance hanger for me (that could bid to maintain other airlines aircraft).
2. build baggage handling, catering, (anything else) (that could bid to service other airlines).It verges on setting up a service company only, but that is part of the airline industry, isn't it?