1.a. Inventory Management: Unlike in CODS (Wiz 7), in Bane, you cannot drop "essential" items, even after you no longer need them. This can create the inventory management problems you refer to. In practice, however (and trust me, I have lots of practice with Bane) this is only an issue with verysmall parties: 2 or 3 characters. When I am running such a small party, I typically avoid a number of these "essential" items. I supppose one could take along a "dummy" character to act as a pack mule, but for me, that defeats the purpose of having a small party. With a party of 5 or 6 characters, you really won't have an inventory management problem, although I would recommend one character with 18s in strength and vitality (for maximum encumberance). Dracon or Lizard fighters are good for this role.1.b. Deleting Characters: short of hex-editing (a very simple edit), you cannot delete characters in Bane or CODS. (Interestingly, these two Wizardry games are the exception, rather than the rule: in all of the other party-based wizardries - 1-3, 5 and 8 - you can add and delete characters; although in 8, you cannot change the initial party size.)
1.c. Class Specific Items: First, you should realize, if you haven't already, that in Bane, only characters who are currently bards can use musical instruments. (Each of the last three wizardries seems to follow its own rule on bards: only bards can use instruments in Bane; anyone who has been a bard and acquired musical skill can use instruments in CODS; and anyone who has been a bard can use musical instruments in W8, up to a point, but only bards can increase their music skill.) Second, other than the Poet's Lute, no class-specific items merit this sort of extra effort. The katana and wakizashi are available for purchase quite early in the game, and while not common, ninja armor can be acquired from at least one of the chests and from monster drops (ninjas, assassins, chunin, grandfathers) in the end game. Furthermore, once a ninja's stealth and level are high enough, the armor is really superfluous. (Side note: according to the coding, it is theoretically possible for dwarves to drop a poet's lute, but the odds are less than 1 in 100: a 10% chance of dropping something in a list of 58 items; in practice, no one has ever reported this occurring.)
2. Locks that you jammed (i.e., they were not jammed the first time you tried to unlock them, but became jammed after you tried to pick or force them one or more times) can be unlocked with the right key or type of key, or with a successful knock-knock spell. I don't feel bad about giving a very minor spoiler in a game that is probably older than some of those who now play it: iron keys will unlock doors on the ground level and barracks level, as well as the locked door on the second floor of one of the corner towers; copper keys will open locked doors on the second floor of the castle. Locked doors you encounter later in the game (e.g., along the River Styx - well into the mid-game - you'll find your way there, eventually (c;) are not affected by these keys; you'll either have to get lucky picking them or cast a successful, high-level knock-knock. Locks that start jammed, before you even tried to pick or force them, can only be opened, if at all, with a key or item specific to that door. One example of this would be the doors in the castle spires with spades on the locks (if you haven't found the first of these, yet, you soon will: it can be reached very early in the game).
One final note: welcome to a great game! I hope you enjoy Bane as much as I have (and continue to). Feel free to post additional questions, although if you apply yourself, you should be able to figure out the puzzles on your own. We'll try not to over-spoil you.