How to set player specific spawn points in Minecraft? (PC edition, of course) [duplicate]

Question

More specifically:
I don't want everyone spawning at the same place, I want it to not need to know who's playing (so "spawnpoint playername x y z" won't do it).
I guess I'm thinking that when people log into the game it senses this person logged in first, they are player1, the second to log on is player2, etc.

Thus it would spawn people in respective spawn points:

spawnpoint player1   -100 10 -100
spawnpoint player2    100 10 100
spawnpoint player3    100 10 -100
spawnpoint player4   -100 10 100

The map i'm making should spawn each player in separate places, while part of the goal is to meet in the middle.

Also, if it matters, the game is for 4 people only, no more no less.
Players can't leave spawn points until each has signaled he/she is ready. so somehow I need to set up a ready count of 4 to let the game begin.

Answer 1

Setup a central Lobby where all players will spawn as usual (/setworldspawn)- they will be all in one room.

This room will need to have 4 pressure plates (best to be separate so every player will be alone on it and others will not be near him). You then need to connect redstone from those plates so it will do AND gate - if all 4 plates will be triggered, the redstone signal will go toward commandblocks (HINT: Use inverted redstone torches -> another torch). Then you need 4x2 commandblocks with the teleport/spawnpoin commands:

/spawnpoint @p[x=X,y=Y,z=Z,r=2] -100 10 -100
/tp @p[x=X,y=Y,z=Z,r=2 -100 10 -100

Where X,Y,Z are coords of the pressure plate. Be sure /spawnpoint executes BEFORE /tp. You will need those two commands for each player, so total of 8 commands.