I did a little research , And as I understand, most of the new games are using MAYA as level editor. For example: DINO CRISIS 3(capcom), new LUCAS ARTS titles, I think DOOM3, GRAN TURISMO 3................... So if MAYA is good enough for those great titles, is it good for me? I want to be capable of creating levels like unreal2's, halo's, or any other new 1P-shooter. And: Is it hard to code a translator such that translates level maded on maya into my 3dengine ???

As long as your exporter or a tool you have can build your map into the proper form the engine needs like BSP Maya could make a decent level editor.