1. You only need (at most) 3 weapons if you're playing properly. Unless you are carrying extra BFGs (the only weapon that holds more ammo than the normal ammo stack does) or overloaded plasma rifles, there's absolutely no reason to have any more weapons than that taking up space in inventory. For example, I'm not really sure the time saved by getting that extra rocket launcher out of your backpack instead of just reloading was worth the loss of an extra inventory slot.
2. Part of playing properly IMO is choosing one of the three basic weapon paths for any weapon-enhancing traits you take and sticking primarily to said weapons (that is, IF you try to put more points into weapon skill traits). These are bullet-type weapons (pistols, chainguns, and plasma rifles), spread/explosive weapons (shotguns and rocket launchers), and melee weapons. Reloader primarily benefits spread/explosive weapons due to their long reload times, EE primarily benefits bullet-type weapons due to the large number of missiles hurled and the fact that damage done primarily depends on most of the bullets actually hitting (whereas spread weapons always hit anyway and aren't affected at all, and though explosive weapons do get a significant benefit as well this can be mitigated somewhat by the presence of nearby walls), and Finesse is fairly good for all weapons as while the effect by itself is small the change in speed can save your life in some cases. Of course, if you stick to defensive traits, this isn't the most helpful tip... :P
3. This death actually seems along similar lines to a lot of my deaths, though instead of having lots of overloaded plasma rifles I have a lot of medkits and die after taking a chance on a miss or kill. The common problem in both cases is that we both said "Nah, we need this for later, we can survive this now even though it might look bad," and promptly died. The solution, obviously, is to use what we have to stay alive as long and as effectively as possible even if there's a chance of surviving without doing so. But then, easier said than done as usual....