I've got Vic from Metzger and done all the other quests I could find. Now do I free the kill Metzger and free the slaves? What are the best weapons to give Sulik, Vic, PC at this time? Should I leave The Den , wonder a bit, then come back and take on Metzger? Or what?

It best advice to carry on for now, come and wipe out him later. You anyway have to return for the car and some other minor quest if I remember right.

While it is possible to take on him right away, it may not be easy at this point - you have to fight his whole gang,.

I had read about technique to hightail the church fight to slavers, so you have expendable allies.
Also you can camp in a room in building across and try to snipe them from window.
You can go around and try to steal all their weapons (but may need a bit too much reloading).

Or you can even start inside the slavers guild, it was quite fun with manual control of party members enabled (there mod for that, a bit buggy trough, at least was back then I played) could be way too risky with AI followers.

Once I did it with crazy hacked up girl offering Metzger to sleep with me, then slaughtered him in bedroom and fight my way out on could weapons only (but that monstrosity had ~30 perks and so on, so nonsense for fun)

I picked the door locks, then locked them myself, which separates them into three groups (Outside, Inside, and Metzgers 'office') and only one window it's easy to shoot through. Which meant one window I could walk to, toss a (two actually) grenade in to their highly clustered group, then step away from with my remaining AP, before doing the same thing with your gun. Once they're down far enough to break out to the slave pens, pick them off and feed on their tears.

To paraphrase Rorschach "Ah boys, you misunderstand. I'm not locked in here with you, you're locked in here with me."

Morrowind, The Den, New Vegas, y'know, any game that gives me the opportunity to indiscriminately slaughter Slavers, I'm kinda good with that.

Jonnan