You'll need relay bricks.
Lots of HUD-displaying relay bricks.
HUDrelay (One per player, or use PrintHUD mod and stray from VCE a little)
33 onActivate -> Self -> fireRelay
0 onActivate -> Client -> vce_modVariable(DisplayHUD, equals, 1)
0 onRelay -> Self -> vce_ifVariable(client, DisplayHUD, equals, 1)
0 onVariableTrue -> Client -> bottomPrint(EXP|<var:cl:EXP>,LEV|<var:cl:level>,HP|<var:pl:health>/<var:pl:maxhealth>)
33 onRelay -> Self -> fireRelay
PrintHUD should just beEXP|<var:cl:EXP>,LEV|<var:cl:level>,HP|<var:pl:health>/<var:pl:maxhealth>
To give a player EXP:0 (trigger in some way) -> Client -> vce_modVariable(EXP, add, X) //X is the amount of EXP to add
0 (same trigger) -> Client -> vce_ifVariable(EXP, greater than, X) //X is the amount of EXP for a level up
0 onVariableTrue -> Client -> vce_modVariable(EXP, set, 0)
0 onVariableTrue -> Client -> vce_modVariable(level, add, 1)