[vdr1981]

Here's what I learned about airbases and planes in SH5...

Are aircraft (or any other AI units) able to use their non-visual sensors for spotting other AI units, or they are only effective against player's boat?

I'll test this and let you know...

For airbase-spawned aircraft, do they need to be in the same base and/or airgroup to act coordinately (i.e. a group of bombers with their fighter escort)?

I never saw such behavior in SH5. Spawned group of airplanes is always made of one plane type...If that's what you meant?

For airbase/carrier-spawned aircraft, is there any way to make some classes not to spawn at night or - conversely - to only spawn in night time?

I don't think so, only nighttime modifier from airstrike.cfg which effects SH5 globally.

For airbase/carrier-spawned aircraft, do they inherit their veterancy level from the unit they spawn from, or how else is their veterancy level determined?

I was wondering the same. My guess is yes, but it's only a guess...

Has anyone tried adding one or more airgroup(s) to any non-carrier sea unit? That would be useful for simulating CAM/MAC ships and scout planes aboard cruisers and battleships.

Hm, that's an interesting one... In theory this should work just like normal AC.

However, It's important to note that when TDW patches for AC are activated, AC will indeed spawn aircrafts when you are detected but the planes will simply roll of the deck and fall in the water...
Regardless, AC will still regularly spawn planes even without TDW patches enabled but only while outside of players 3D rendering range (40 km by default), just like "moving" airbase.

There is also one more very important and ugly bug about airbases in SH5.
Inactive bases will spawn planes even before airbase activation date if there's axis threat zone up to XXX miles away (in addition to sea traffic avoidance,opposite threat zones are used as a patrol zones for planes as well )! For example, Airbase in Azores, which should become active in 1943 IIRC, will spawn planes even in Happy times campaign as well, well before airbase activation date. If such planes enter players 3D rendering range the game will most likelly CTD and if saved before that, the save will become corrupted.

There were a lot of these conflicts in the original OHII files but I managed to solved them somehow in Wolves...