Wish I could help Doobs. I'll be away for Annual Training with the Reserves during Operation Downfall, and I'd have easily taken IJN side for the senerio.
Ki-67's and Arados......
Ki-67's are fast, but take a lot of time to get up to speed. You want to be lined up on target at least 30 miles out with newbies, in order for it to steady up.... and be at level altitude at least 40 miles out as well (yes, can be done closer buff drivers, but I'm considering the quality of pilots Doobs is likely to get). Ki-67 used to be a favoite pork buff, until mass resupply efforts became all the rage in MA. You could get over and hit dar or troops at several bases fairly quickley, and get out again.
I usually don't take them over 14K, but usually at least 11K. Senerio map may have a wind layer, many do, so just under that by 1K might be advisable. Ki-67's make their best speed at around 20K altitude (and their climb rate really sux above that anyways. Best to climb to the desired altitude while still over friendly airspace, as the difference between climb speed and level flight is pretty great. Remind pilots to take off with flaps up.
Ki-67's have very little climb creep when at full speed and level, unlike heavy bombers. They must be lined up well ahead of time (F3 view, zoomed... use F8 to pan, and pan to view target from behind). Slight adjustments close to drop point throws off the drones' impact point. They are slow to reform. Small adjustements well ahead of the drop point are best.
8-100kgs (1,760 lbs) is best bomb load for this bird. Adjust the delay as neccessary, but if hitting a point target, leave at 0.05 to drop. 3 planes, that's 5,280 lbs total..... nice hit on a CV.
Ki-67's also have great fuel range. If you need to start in rear and get to distant target to avoid fighter sweeps, it can do so. Looks like you are limited to 2 fields though with Ki-67's
They are fast, and can be hard to intercept, and have a decent defensive armament.... but share a defensive blind spot to their belly like a B-26. The 20mm dorsal is fun to snipe at planes trying to get above you to dive down on you. Ammunition is limited, like most buffs. Turrent turns while in gunner position work well to bring low trailing figher into arc of guns.
As a torpedo launching platform..... I'd stick with bombs..... torps are very hard to master in this game, and keeping a Ki-67 that low and slow is suicide.
Ar-234. Sez a limt of 10 per frame.... is that 10 individual Ar234's or 10 flights of 234's per frame? Hope its formations.
Formations should be open in this senerio map, and Ar234's should be used in formations, if allowed. Only time I use Arados is generally to killl a CV. Gotta spend buff perkies on something, so I lift formations of Ar-234's for this. Climb to 5 to 10K (depends on how much flak I expect to run into. Drop full load 1 CV length out in front of the carrier. Dead carrier. The lower the better, since it cuts down on the lead to target and their reaction time, but always remember the flak.
Also take time to get to full speed once level. Give plenty of time/distance to do so.
Again, do your climbing well ahead of time over friendly airspace, then level and head to target. Salvo 3. Delay 0.05. Try to save the JATO rockets for the escape. I save some tail gun ammo, just to scare off pursuit.... and you might get lucky with it at times.
If used en mass, from a distant field, you could consider the DT option, but unless fuel use is pretty severe in this map, using 3 500 kg bombs (3,300 pounds per plane, 9,900 if in formations) is the better load. JATOS are for evasive dashes. I nearly always take 100% fuel in them.
Landing any jet in game takes a little forethought and patience on the part of the pilot. If you can get experienced Arado drivers, use them to land and rearm as often as they can..... these are your best ship killers from the plane set I've seen. They don't even have to kill every CV they drop on... one hit is lots of damage, which can be followed up by Ki-67's, Kates, and Vals.
For both, go in a medium altitudes. Be at full speed well in advance. Line up on target well ahead of time. Use slight course changes on the run to keep drones on target.
A few flights of each, from different directions, over a target ship should easily take it down. Comes down to if CV's will respawn on map as to whether you can down enough of them fast/often enough to get ahead of the Allies.
Both can be used as ship killers. Ki-67 may have better load and bomb spread for towns, should you need to take one back. Both can knock out 1 to 3 hard targets such as hangars, per sortie.
But in multiple passes, it takes a ot longer to get turned around and back on target then with heavy buffs..... you need to allow time for the bird to steady up again. Better if both bombers are used as one pass, or passes over seperate targets.... rather than multiple passes over one target. Much easier for the pilots who will be flying for you.
If you can coordinate with missions of fighter, dive bombers, level bombers, and torpedo planes, they should be very effective against allied fleets. Scout early, fix position of enemy fleets, mass attacks against a few of them at a time, from multiple directions. Again, comes own to fleet respawn or not, if you can keep ahead of Allies. Torpedo raid goes in, drags cap down, buffs and dive bombers go in.... that sort of thing. Vary your plans, mix it up, don't get predictable.
You also get use of Kates and Vals.... but they will need a good escort.... to use in conjuction with the buffs.
Biggest disadvange is your fields are already public knowledge. Two field flatteded can deprive you of all your buffs.
Ki-61-KAIc is your best scout platform..... lots of fuel, good speed, good range. Use them to get the buffs and attack forces over target.
Those are my thoughts on the subject.. Don't know who to recommend you try and enlist for the Special Event. Any corrections or thoughts on these observations from the peanut gallery? At least the IJN is recruiting faster than the Allies are.