Replied your pm.
I currently have build for hbg glutton tank and dps cluster.

normal or extreme behemoth ?
I would highly recommend play with a tank, it just makes life much easier.

I can play as tank or cluster dps role
Normal behemoth if can be cleared with just 3 players (1 tank with 2 cluster dps).
Extreme behemoth is a totally different beast, definitely need a team of 4.

Any weapon is fine, just attack his hind legs and careful when he do his spin move if you are using melee.
I manage to clear normal behemoth with another friend long ago, 1 CB and 1 lance, took us 30 minutes though haha.

I did some behemoth run yesterday with a group of friends, around 13 minutes per run (1 tank 3 cluster).
Usually I will online around 10pm-1am on most days.
Pm me your psn id if you need a buddy to fight behemoth, I’ve cleared almost everything and just waiting for new events these days.

Check your psn, I've added you.
Do you have a tank build with KT Glutton ? Guard Up + Ironwall 5 would be perfect to tank with Glutton.
If you don't have then it is ok to run KT LBG or DB as dps.

If we have 4 players, I would advise give extreme a try as well, since the event is near its end.
Normal behemoth is available all the time, so no rush on that.

This is strange.
I'm using the same LBG with thunder ammo and I'm moving a lot to chase kulve tarroth.