Hi and welcome to the forum,
How to import a world and how to install plugins is already answered in our FAQ.
You can turn on command blocks in the worlds world.ini [Mechanics]->CommandBlocksEnabled
If you have the Core plugin enabled then you can rank yourself, change gamemodes and use /give and /i
EDIT:
I forgot to explain how to generate flat worlds. You do that by going once again to your worlds world.ini and changing the values in [Generator] to the following:
How to import a world and how to install plugins is already answered in our FAQ.
You can turn on command blocks in the worlds world.ini [Mechanics]->CommandBlocksEnabled
If you have the Core plugin enabled then you can rank yourself, change gamemodes and use /give and /i
EDIT:
I forgot to explain how to generate flat worlds. You do that by going once again to your worlds world.ini and changing the values in [Generator] to the following:
Code:
BiomeGen=Constant
ConstantBiome=Plains
HeightGen=Flat
FlatHeight=5
CompositionGen=Classic
ClassicSeaLevel=0
ClassicBeachHeight=-1
Finishers=