Hrm...well let me see if I can answer these for you:
1: There are numerous types of planes, but since its carrier we're talking about there is 4: fighter, dive bomber, torpedo bomber, and scout. Fighters are plane that protects your attack squadron and gain air supreiority over your adversaries (thus enabling your ships to do their spotting attack). Dive bombers and your torpedo bombers are your carrier's attack power, the better the plane the more damage. Most people choose torpedo bombers due to better performance and damage, but keep in mind that your attack planes can be shot down and when all your planes are gone your carrier is basically useless and you will have to retrain your aircraft. Lastly the scout, they basically increase your line of sight and if you have a saiun in your carrier it prevents red T.
2: Reppuu mule: You stuff a carrier with a bunch of fighters, namely the fighter reppuu where it's craftable, and they basically help you gain air superiority though they won't be able to attack anyone.
3. In most situations you will want to use CVL, since most AVs can only use seaplanes and have a smaller plane count. I recommend leveling chitose and chiyoda to CVL kai ni, and if you can also train up junyou.
Green: Gives fighter power, essential for aerial combat when fighting the enemy. Helps shoot down enemy's plane. If you don't have enough, your planes will get shoot down a lot and you'll lose a lot of baux (+ other factors). Applies to the two planes below. It is ESSENTIAL that you have some of these if the map has CV. Check what their Fight power (FP) is and get more than them by 1.5 times for Air Superiority (see above). CANNOT ATTACK SURFACE FLEET. Only attack Planes.
Blue: Torpedo bomber, hits their ships with torpedos, uses torpedo stat. Calculation based on above. Has a random stat multiplier or 1.5 or 0.8. CAN ATTACK SURFACE FLEET
Red: Dive Bomber, similar to Blue but uses Divebomb stat. Calculation based on link above. Has consistent stat multiplier of 1. CAN ATTACK SURFACE FLEET. When equipped on CV, cannot attack Land-Base Boss (Installation)
Repuu Mule: Give a CV Green plane only. If only green plane, can't attack.
AVs vs CVLs: Depends on the situation. Both can attack subs if equipped with bombers. AVs are not CVLs and when Fighter Power is needed most of the time AVs cannot give you that. AVs are not a reliable opening air-strike ship and most of the time doesn't do much. AVs can equip midget subs for opening torpedo. AVs can attack during Night battle as opposed to (CV)Ls. etc. There's other situations.
i was just wondering, does it matter where i put my aircraft carriers in a fleet?
For protection purpose: put as flagship, as flagships have better protection. If you are encountering airstrike nodes the first 3 slots receives more protection.
For Night battle, just like above, put them in the last few slots.
Note that since in a combined fleet only the 2nd fleet participates in night battle, carriers in the 1st fleet doesn't have to worry about night battles. Rather, since we wish to have the carriers attack as early as possible (esp. in the second round of shelling) to prevent them from being knocked out (can't attack with HP<=50%) before attacking, putting them in front positions is better.
So it actually depends on what kind of a fight you are facing. If you face little to no night battle concerns it is advised to put them as the 1st~3rd ships.