I keep the chainsaw not only because it saves some ammo or can make zerk pack more useful.
You'll often find yourself in melee, and chainsaw has a great DPS (which is even better after UC :). Killing monsters faster reduces damages.
Also, you sometimes want to stay melee (like vs mancubus or spiders). I don't use my usual shotgun in such a case (your HP pistol would have the same issue), and I don't carry ammo for my plasma gun, so the answer is melee again.
About SOB w/shotguns, I think I stopped using 7d3 shotguns when I noticed the HUGE difference it makes for knockback to have 2 less average damages. I always use a 8d3 now (reloading from one of my 3 shellboxes doesn't take more time than pumping anyway, and my doomguy is most of the time already OP by the time he could craft a tac shotty)
I was quite sure the damage was added after distance reductions, so I'm not surprised that it works so well. I thought the treshold was 12dmg, but anyway, what counts is that some levels in SOB make the difference. I don't care about the numbers too much.
About inventory, I always keep a phase device when I can. Sometimes more, up to 3, but ammo will usually be more useful. It can get you out of *really* nasty situations. (tip : When you don't have one, think of using rocket jump. It's ideal for situations like... anomaly ambush whel playing AoHu).
You're right to dump the BFG. I always keep it because... it's fun, thematic, and nice, but barely ever actually use it (even in the mortuary, where I rush to the nuclear one instead --sometimes using rocket jumps--).
I usually keep 2 skulls for mortuary, but rarely use the 2nd.
I only carry one suit for the pits/Erebus. Taking some damages when running through some titles of acid / lava is not a problem.
I take thermies "because they are cool", but use them as fast as I can. I nuke spidey the guaranteed way, with the nuke BFG from mort. Alternatively, you can try to keep one for Cybie, or UC... but it's highly unreliable. From a pure "efficiency" pov, I think there's no real reason to use them. You rarely need them, and the can make you miss stuff.
I always carry the staff (I'm a YAAM/conqueror/JC guy)
I avoid carrying unused mods. I know what I need most of the times anyway, and rush WK to max mods usage and save slots. Once my shotty is already P2 or P3, I put P on armors. A are for tac boots, then armors, B for Tac RL / (nanomachic or unused) plasma gun, then (unused) BFG, and T are for decoration.
I also thought I avoid carrying useless weapons but when thinking about it... I use mostly shotty / Chainsaw and RL, but always carry a plasma gun and a BFG, and sometimes keeps the missile launcher until HoC.
I usually have one extra armor (and sometimes up to 6/7 unused ones in the end, when I find some shielded vests, phaseshifts, Malek, Necro, Shielded... well, that's for decoration too, since I know I won't need them at that point)
I don't use shottyman. It's useless when cornershotting, so I'd prefer going for DM, which will help me reach a safe spot. But aside of that subjective pov, I'd advise you to have "side-disciplines". That's one of the reasons why I stopped using masteries, and nearly always pick BER : it makes me more versatile.
