Hi. I would like to ask about this thing:

Are there some advantages for joining a particular gang?
Can you join only one gang or more?
Are there any disadvantages?

Currently, I know, that you can join the white gloves sociaty and the kings. Are there more gangs?

P.S. Asking, because of the quest with the kings and the favor, hehe.

No just they friends with youm, also some companions are effected negativly by which fraction you join or kill

I believe you can join the Brotherhood of Steel and become a Paladin.

I am a Paladin in the Brotherhood of Steel. Did all their quests and got the Power Armor
The only problem with BOS is that you can't enter areas with OLDER Power Armors that say Brotherhood in front (2 shoulder pads), The new model has only one shoulder blade. The Reason I say this is that everybody will attack you on site and if you attack back your Karma will go to @#$#@$#$. I had to rerun a previous save file as I was Hated by the NCR even tho they shot first.
Now I fixed my new armor and I have no problems at all. I am liked in most towns except of course the Legion who Hate me to hell! hehehe....

So advantages/disadvantages - hatred/love from certain factions, if you join any.

Any other advs/disadvs?
Can you join more than one faction?

What if you join the great khans?

You can't join anyone, there's is no game mechanic for doing it. You might get a title like "Paladin" and you can wear faction uniforms to roleplay a bit, but ultimately you're still your own man.

It's all about reputation.

kille the ultra luxe they eat ppl what happens if they are hungry and you are the only one around....you become dinner....not true but that was my fear so i killed em all...after all the quests they gave me hahaha

Okay, thanks for the information, Duskey.