Default ones are perfectly fine, IMO.
Default weapons are awesome. But having custom weapons will add to the effect of the mod. In the old "Heat RPG", it was just scripts and a heat bar, nothing really visible. If there's cool new weapons, the mod'll be much better.
I have a rifle, shotgun and maybe a pistol ready to go (just needs to be exported). Oh, and I have this auto I posted somewhere a while back (The one laying on the ground). Here's the rifle. And the shotgun was posted on this topic some pages back. I just checked for a pistol and I do not have one that would fit this gamemode. So specify a model and I'll give it a go.
I think all of those would work great. As for the pistol... I dunno. Googling... okay I googled "survival pistol" (lol) and one of the pics it brought up was this...

Your models are, as always, extremely hawt. That SIG 550 and the 560 are sooo hawt :O
I think it fits the theme well enough. It would be very cheap compared to other weapons, as it's very small. Emphasis on small, that should be the main feature of the model :3