Where is the afk spot / which biom?

I built a creeper farm on a minecraft server. There's a farm in the void, I can change the biom. Which biom should I make for a creeper farm?

The farm starts at height 101 and ends at height 133. There are 4 towers in a circle, (photo). They converge towards the middle with water. Now I would like to build an afk spot. I was thinking of the center point in the middle? At what height should I build the spot?

Green = creeper farming

Blue = watercourses

Red = is the middle.

All farms are built in the same way and parallel to each other.

Which biom should I make for a creeper farm?

The biome is completely irrelevant in terms of efficiency. The main thing is that creepers can spawn in it. So everything goes except Nether, End and Mushroom Island.

At what height should I build the spot?

You have already realized correctly that you should build it in the middle of the farms. Regarding the height:

How far are the spawn platforms from the center?

If they are more than 24 blocks away, you can easily do your AFK spot at farm level. Just in the middle in between.

Otherwise (if the platforms are closer than 24 blocks to the center point) the AFK spot must be at least 24 blocks above (or below) the farms. (So at height ~ 160)

Yes, the space between the farms is 30 blocks

So 15 blocks from farm to center?

This is too little. Then build your AFK spot at height 160. Or height 70. Depending on what you prefer.

Uh, every farm is about 30 blocks away from the middle, sorry I spelled it wrong first

Oh yes, then you can make the AFK point at the level of the farms, just in between in the middle.