The new base rules in game 3 certainly help with the regional airline format. The real problem is restricting your airline types, initially 17 pax a/c are about right to get a network going and Company Image up towards 20 with 30 to 40 seaters as routes and cash allows. Buying v leasing seems to be about 1/3rd owned but can be anything, depends how often you want to tweak prices or grow a/c numbers. By week 20 + you'll be looking to buy jets to shift more routes per day and extend your range of operations. That starts to get expensive and it's wise to buy types that will last and develop, not some short term manufacturer that will go bust or never make another a/c type that's compatible with your existing fleet.
It works for me, now 30 weeks in and more or less viable as the industry moves towards Jets, but still plenty of competition from the smaller/poorer airlines with Twin Turbo/Piston Props over ten years old.