Yora, this is a huuuuuuge complicated question that occupies the brains of many many people, some of whom actually make a living writing these things and are still wrestling with the things you bring up.
So, some advice:
• All the appendices of the original 1st ed. AD&D DMG.
• As much as you can on the blogs Henchmen Abuse (creator of ASE), Dungeon of Signs (lots of cool old-school adventures, several set in ASE land), Hack and Slash, Playing D&D with Porn Stars (Vornheim), False Machine (Deep Carbon Observatory), Roles, Rules, and Rolls, and Goblin Punch.
• Also, Bryce Lynch's reviews at http://tenfootpole.org/ironspike. You might not agree with everything, but there is a lot of practical advice about how to set up an adventure for best use by DMs and what is valuable to both players and DMs
• Some of the classic AD&D mods: G1-3, D1-2, B2, X1, X2, B1, WG4, S1-4, L1, L2, N1, I8, I9, A1-4
• The Workshop forum over on Dragonsfoot
I don't know, that's a start. Maybe you've read it all already!
Here's a fun experiment: First, try creating teh dungeon and map by slavishly following the procedure on random dungeon generation in the DMG. After you've filled a page or two, stop. Go back a couple days later and find what's cool about what you have and what you might want to keep and what really doesn't work. Throw out some of each and then make it your own.