I like this idea allot. I think your secondary ideas (bullets 1 thru 4) are good starting additonal thoughts at this point until you’ve tried to play a few games with the initial ideas/concept to see if the Colonial Outpost is too strong for the Allies or not enough help for the Allies.
I surmise that just the CO might not be enough for the allies, though.
So to your point about the CO as part of a bid, I propose that the side that has the advantage (in AA50, the Axis) bid progressively larger amounts to give the weaker side (Allies in AA50) to have the ‘stronger’ side. For example, I will take the Axis and give the Allies $10 (in bid units or IPCs). Opposing player may believe he can still win with the Axis giving up more than $10 IPCs, so he says he will take the Axis and give the Allies $15 (in bid units or IPCs). This goes back and forth until the Allied play accepts the extra units.
Instead of starting at $1 IPC and bidding higher, the starting bid for the Axis is the Colonial Outpost (as described aboove). Now the opposing player can bid for the Axis giving the CO + $3 IPCs… on so on.
So, should standard bid placement restrictions would be in play (like 1 unit per TT?) I believe you should be able to put one unit with the CO complex.