OK so I think I've worked out a system....
The year is 2003, so at the start the mainline a/c is going to be A319s. Why don't we start at opposite bases, IE: me at JFK and you at LGA, with A319s running mainline. Once you earn enough cash to purchase 5x Embraer ERJ 145XRs (110 million Euros) of any variant, shutter the LGA base and sell me the A319s, as well as shift over to JFK. We'll go from there. The way I'm looking to operate is A319s, A321s, and then eventually A332, and A342 mainline, which you can help out with as you'll have more cash. I'll operate to 750k+ airports and you to all of those below that threshold. On the a/c side, lets stick to E145s @ JFK, MCO, and CLT, and E140s @ LGA, BOS, and IAD. For routes of distance > 1000nm, use E170s for realism sakes. Frequency wise, airports with <500k pax, use 2x, 500k-750k 3x. For me, it'll be 2x to <10,000,000, 3x to <30,000,000, 2x A321 for airports >30,000,000