I don't like the BoS, the Institute or the terrorists of the Railroad. BTW I also don't like the Minutemen but that's more because of the tedious settlement stuff and Preston's talk that's so sweet and slimy that I get caries from it.

Do I need a certain number of settlements/artillery/minutemen as help to destroy the three other factions? I don't intent to have more than two settlements at all that I support (and that's 100% more than in my first play session).

Once I wandered the world at low level and a mean looking Deathclaw appeared near me. Luckily at the same moment three BoS PA-guys on patrol with gatling lasers rounded the corner and made short work of the monster. I'm a bit afraid to battle against these guys alone. Will the minutemen be of any help?

I'm fairly certain that if you want to do the main quest you'll eventually have to side with one of them. Eventually you'll be able to take out anything that gets in your way but I'm pretty sure you still have to side with someone.

You do have to side.

I guess F:NV spoilt me with Yes Man but ultimately you have to stop playing it down the middle and choose a side.

For what its worth my attack on institute went amazingly well, I even led a tourist party around who kept yelling at things

Spoiled us with Yes Man, and with being able to ally varying competing factions against others.