Exclusively "fighter" bases can be done by "cloning" the existing "LAB_SmallAirBaseGe" and renaming it something like "LAB_FigherAirBaseGe" or whatever. Don't forget the Roster file, and to re-map the IDs of the binary files. You then take the Land folders cfg file, and limit the AirGroups to a fighter plane or two - don't do too many. You could also "date" multiple AirGroups, like on the CV in the game.
The thing with "fighter" aircraft is "no, they do not fight each other"... a massive oversight on the devs part. In SH2, OK, understandable. SH3 is stretching it, but to bring the ~same~ krapp into SH4 is inexcusable... while "accurate" AI dogfights would be difficult, the least they could do is shoot at each other on their way by... My guess is that, similar to the way planes will attack a ship until they are a flaming fireball and/ or shot down, similar probably happened if they go to attack each other, in that ~that~ would be all that the planes would do... all of them, including level bombers...
Now, another thing to remember about AirBases, is that if you happen to "see" an enemy target (which can happen without your periscope being raised, but at periscope depth, since the XO counter-manded your "do NOT raise the periscope!!!" order), and there is an AirBase within range, the airbase will send a "response" your way, whether you fone home or not. When you use the grease pencil, you are specifically telling a "scout" plane where to go. Look through some of the Land folder things that lurker did with the original OpMonsun, which are still in Dark Waters, and you'll see examples of some of his cloned airbases. He has some for specific air groups at specific time frames in specific locations for the mod. He also cloned the air base that is controllable by the grease pencil to restrict it to certain planes at certain locations and time. I do not know if you can control fighters and regular bombers the same way, but I have never tried...