"What gamemode etc. would be fun to play, and what should be required to be supported by the map (default game modes).", As posted on the main pages comments by Quantum 1000 is the main subject of this title. We need to figure out how each default gamemode will be suported by each map and what we will have to put into the maps. Also, what items will be used in each gamemode.
Here is a list of the default gamemodes:

CTF, Capture the flag: You have to go take the enemys flag and deleiver it back to your base untill the enemy does not have any more of their flag.

HHM, Horseless Headmen: This is a game based of a meme the Headless Horseman, but in minecraft we dont have horses and we have heads so its called otherwise. One player plays as the HHM, and has to kill everyone else. For he gets higher armor and no weapon (maybe) which makes him more powerful then everyone else, so the players must work together to kill him.

FFA, Free for all: Everyone goes against eachother and fights till the time limit has been hit.

TDM, Team death match: Exactly like FFA except there are teams.

CA, Clan Arena: Exactly like TDM, except there are 10 (may be decided otherwise) rounds per match, and when someone dies, they are out of the game for that round. When everyone has died on one match the surviving team wins.

A/D, Attack and Defence: There are the two bases, alike in CTF, but each match, one team defends there flag, and the other team has to try to cap their flag. Only for 1 wool (one part of the flag, one cap.)

VIP, Very Important Person: GET TO THE CHOPPAH! Well, the base. One team, consisting 3 or less people, are guiding the VIP to their base (they will be placed near the enemy base). And the other team, has to kill the VIP.

INF, Infection: Zombies! Two people start out as a zombie (they hold green wool to be identified) and they have to attack people then hand them 1 green wool, to spread the infection. The rest are the humans, and must kill all the zombie, with wooden swords! (may be changed in discussion).

Those are all the default Gamemodes, but there are two more that must have specific maps to work with the gameplay:

STF, Spleef the Flag: Its CTF, and Spleef! Instead of killing eachother, you have to spleef one another with shovels on the snow. If you don't know what spleef is, your kinda a noob. jk, lots of people don't know it, just google "minecraft spleef".

RnS, Round n' Shoot: There is a rail system that goes in circles spinning people in minecarts, and you have to kill eachother with bows while spinning in the carts. (btw, there arent teams in it.)

That describes and names all of the gamemodes thought of so far. Please comment to discuss the situation.

Hello! [This is not a announcment, just a discussion, so please comment.]
The basic rules we are trying to get is, whats the flag going to be, how many blocks for the flag, how to make the flag, what items to give the players, and all that sorta stuff. Anyways, please comment if you have ideas.