V:5 starts with you surrounded in the middle of of a four-quadrant map, the guards surrounding you are of the type you've fought before in the vaults, however if you get bogged down fighting them, you're going to attract attention from every which way, all four quadrants of V:5 are packed with a lot of tough monsters, nothing you haven't dealt with so far, but there's just *more of them* also there's very very few 1-corridor-wide places, none at all on some maps.
There's a 3 corridor wide hallway between each of the four quadrants leading N/S/E/W and a 2 corridor wide hallway along the edges surrounding the map, each quadrant has an opening at the center, and one in the corner (the contents of the quadrants vary) what you want to concentrate on is *not getting overwhelmed by sheer numbers* there are a couple different tactics for doing so:
1. Break through the initial welcoming party (either blink or fear) and make a break for one of the side corridors (doesn't matter which they all are the same, use haste to avoid taking much damage while fleeing) once you're in a corridor (you want to be about halfway between the central corridor and the corner of the map) *and only then* do you start hammering away, the welcoming party and most of the quadrant you're closest to, with any luck you'll take care of the following party from the center before the group from the corner arrives en-masse. If you get into any trouble at all *teleport* and do it early, like before you're remotely at risk, you'll end up somewhere random, but keep in mind critters are heading towards the last sound they heard, so towards the center (from your arrival) or towards the place where you were last fighting, hopefully you'll land somewhere away from all the nastiness, and only have to fight a couple things before being able to rest and reposition, if you end up in a bad spot, TP again.
2. Start with the teleporting, ignore the welcome party (or blow them up with some kind of initial attack in some fashion) it helps a lot to have magic mapping, so you know if the spot you land in is decent, otherwise you're just starting with the 'If you get into trouble' part from 1.
3. Try to stairdance the welcome party. This works amazingly well, *if* a warden doesn't lock the staircase on you, to stairdance the welcoming party, you want to pull them, in groups, upstairs and beat them up there, rest, go down, and pull up another group. Wardens make this annoying, as they can lock the staircase preventing you from going up. If they do that, you either need to kill them asap or have a plan B (possibly one of the above) The problem comes if you spend too long at the bottom of the stairs fiddling around, the *tougher critters* from the quadrants will start to arrive, and they can be harder to escape from (so if things go sour, you may end up needing to escape and it might take several risky teleports to do so)
For 3. The risk is more variable, and will only very occasionally make things horrible, most of the time it will be significantly easier than the other two, 1. and 2. are more consistent strategies, and will nearly always result in the same amount of difficulty, harder than the "easiest" result of doing 3. but easier than the hardest result of doing 3.
Things that help a lot: Area effect damage (wand of clouds and cloud offense spells are amazing in the corridors) axes, javelins, bolt spells, anything that lets you do damage to a bunch of stuff helps. Regeneration, any kind of passive healing (Gods, plain old being a troll, etc.) not as important as it is in the abyss, or hell, but getting a break from combat to rest requires a lot of effort in V:5 (at least until you kill everything) Shields are slightly less effective than they are elsewhere, but still pretty good. You want to have rN available to reduce the damage from shadow dragon breath, and preferably rElec for titans and blue dragons, as well as rF and rC for the more common fire/cold giants and the various weapons you might face. If you're missing a resistance of some sort, you will need to be aware of it, and emphasize killing off that sort of critter quickly (preferably at range with some sort of peircing attack) even more true than it is elsewhere, you need to prioritize convokers (to prevent more critters from arriving) and sentinels (because they will mark you, and that pulls *everyone* to the party, and you really don't want that)
Having MR+++ reduces the odds of being marked by sentinels to a low level, usually you can kill them before they mark you with MR+++ (with MR++++ marking is no longer likely enough that you need to worry about it) with less MR, you'll probably be marked almost instantly, and you'll need to be aware of the fact that you're marked and flee early and often, until you clear it and get away from the area.
Note all this presumes you're "normally" powerful, if you're super overpowered, you can just like blow up everything with no effort, and if you're underpowered, you're going to have a hard time and struggle pretty badly, and probably die (You might die even if you're "normally" powerful, pay attention to everything on screen at all times and you'll probably do OK)