It's hard to say based on the mortem, but it looks like you didn't have all that much ammo going into there. If you're seriously pinched for ammunition, DO NOT try The Mortuary (with the obvious exception being MAc), it's just not going to work out very well. If I'm planning on using energy weapons, ideally I'd like both BFGs (with some bulk mods for extra capacity), as well as 4-5 stacks of power cells. If you have a missile launcher, anywhere from 30 to 50 rockets is a good number. Shotguns should come in with 6-8 stacks just in case they can't resupply during the slaughter, chaingunners (although it should be more like a TH'd assault rifle or assault cannon or P3T2) should have 8-10 stacks. If you're actually attempting it with pistols only, have as much as you can afford to carry without becoming too short-changed for healing and enviro.
If you're lucky with positioning or spawns or whatever, you won't actually need all of this ammo, but you should really go into the Mortuary with an overkill perspective in mind. It's way too easy to get swarmed there, so you need to have big guns AND big supplies. Don't worry about the Arch-viles respawning, they won't, so focus-fire them (with explosives if there are a lot of guys around) and it'll take a lot of the pressure off.
Regarding too many weapons, if you find yourself strapped for inventory space, non-vital weapons are often a good option. Sometimes it means you can get rid of all the ammo that goes with it, freeing up even more room for your other ammo types. (As a rule of thumb, it's good to keep rockets and BFGs, but try sticking only to bullets, shells, or cells as your primary. Rapid-fire builds should keep one energy weapon and one bullet weapon just in case either runs out of its ammo.)