See my note on range versus "Sentry." If history justifies them as having a longer range than two squares on a huge Earth map, then they make sense.
Well, for starters, I NEVER base my stats on a huge Earth map... nor will I ever... because the game itself is not scaled to the huge Earth map.... to be honest, it's not scaled to anything (but perhaps it's own units). If units were scaled to a map, their ranges, movement and everything else would change between scenarios, tiny maps, huge maps, etc, etc.
Simply put, the best way to scale a unit is to compare it with other pre-existing units in the game.
A WWII Bomber (Rng-8) has a longer range then a WWII Fighter (Rng-6)... typically speaking, WWII single-engined light bombers had a range longer then fighters, but shorter then heavy bombers (WolfMod; Rng-7). None of these are scaled off of any particular map, but rather to each other (and from default Civ4 ranges). Actual ranges of seaplanes varied of course, but during WWII most typically had ranges similar to WWII Light Bombers... ergo, that would be their range in-game (7).
On the issue of seaplanes: I think it's a beautiful model, and it would be great to include in a scenario. But I think it's below the scope for a standard CIV game.
I've said before that I usually abstract smaller technological advances into promotions. By the same token, this is one of the things which can also be abstracted by promotions. Why can this battleship see farther than other ships? Because it has a better radar, or better communications, or better intel, or spotter planes/helicopters, satellite imaging, even better training, whatever... there's something from history to abstract at any given point in time. Whatever the abstraction, the battleship certainly cannot see farther because some admiral promoted the crew.
If you want to make more promotions, then I'll be all support, though!
I don't think you can model seaplanes through a promotion... radar probably, but not seaplanes. Radar sweeps in radius around the ship... certainly you could make some sort of "Sentry" like Radar promotion that saw a certain number of squares around a ship, but that does not (would not) mirror the capabilities of a scout plane.
A scout plane files in linear directions... north or south or east or west of a ship to scout-out for enemy forces or troops or whatever. Typical ranges of seaplanes were 600-1,000 miles depending on the nationality/type of seaplane. They were critical in finding enemy task forces in large ocean spaces... Midway was not won because of Radar... Midway was won because US scout planes spotted the Japanese task force before Japanese scout planes spotted the US task force. Both forces would have just been randomly sending out strike forces without knowing where the enemy was, and both forces found each other through scout planes of one type or another. I don't think you can recreate the effect of a scout plane with a promotion.
Mind you... there are already "scout" planes in the Wolfshanze Mod... a lot of nations (especially America) used carrier-based light bombers as scouts (such as the Dauntless), and you can certainly use both fighters and bombers on carriers as scouts right now as it stands... however, everytime I get around to needing/wanting to scout-out for the enemy and I have a carrier handy, I think about how much it cost to build that fighter or bomber, and how that if I use that fighter or bomber to scout this turn, that's one less fighter protecting my fleet or one less bomber able to attack this turn... adding a very inexpensive and combat-worthless scout plane (launched from cruisers or battleships), would be a guilt-free way of scouting by air without sacrificing fleet defense or bomber operations (or sacrificing crucial carrier capacity just for a scout plane... a cruiser or battleship could carry the scout).
Oh, and somebody mentioned scout planes being on WWI Dreadnoughts... well, the capacity would be there, you just wouldn't be able to do it until WWII timeframe (scout planes on ships really weren't common until after WWI, but they were retrofitted to WWI Dreadnoughts). Simply by making scout planes available with WWII aircraft (not WWI aircraft), Dreadnoughts in WWI would not carry any aircraft, but those Dreadnoughts that survive till WWII would be able to carry them (I already thought this angle out).
Oh, and I would probably make WWI Zeppelins upgradeable to WWII Scout Planes... just thought I'd toss that out there.
#1, i'm thinking no. the game promotes combined arms tactics so i will normally use fighters on carriers for recon on oceans and over other continents.
#2, i will answer this be giving an example from one of my previous games. i can't remember in which version of the mod this change was made, but when explorers were beefed up a bit, in my next game, peter the great began using these to defend cities AND as part of his invasion forces. this has since changed, but the point is, it does happen.
This would probably be the best argument to NOT implement scout planes... AI use (or misuse).
This is in-fact my biggest delima that has no real answer, because it would really require a lot of playtesting that you can't just set-up in the WB realistically. Maybe I could just add them to the mod and throw it out there and if folks didn't like it because the AI misused the heck out of them, I'd take them back out again?!?!? It's really not much XML work on my part... it's adding one new unit... adding the Scout Plane special category and assigning it to a few ships.
Hopefully AI misuse would be curtailed by AI "use" tags in the unit info (what the unit is used for) and limitations of bases (can't be used on carriers, only one per CA or BB, and no-more then four in a city, which hopefully will have fighters and/or bombers instead).
Oh, and to address something a little off-topic (but somewhat related), the new use of Explorers in the last release of the Wolfshanze Mod... they weren't made "stronger" per-se... all their stats are the same... but I did flag Explorers as able to make attacks where before they weren't. The AI "use tags" stayed the same (so I didn't order the AI to use them differently either). I have played a game with Explorers having the ability to attack... I had 18 civs in my game... ONE AI did seem to use Explorers quite a bit in a manner not-really intended... the Khmer... but I can't blame them... I was at war with them in the late middle ages, and I had deprived the Khmer of all their useful resources (they had none in-fact... no copper, no iron), so there were only two units they could really build... Archers and Explorers... so while I did see the Khmer with more Explorers then normal, I excused it as a situational issue... I didn't notice any of the other civs over-using Explorers in my game from what I was used to in past experiences.
It has been refreshing to me to be able to use an Explorer to clear a goody hut protected by a lone Str-2 Barbarian Warrior however... nothing more frustrating then seeing totally backwards savages and your Explorer can't get at their gold or rape their women because they're not allowed to attack. I actually like this change, and I can reason-away the Khmer use... I didn't notice the AI abusing Explorers in any other civ.
Oh well... guess I gotta ponder this seaplane thing a bit more...