20 Questions here.
Silver standard, per Dragon Magazine 74 "A Player Character And His Money" by Lewis Pulsipher
Skills, Secondary Skills-
Keeping it simple - just roll on the table in the DMG, or (pick one that fits.)
Spell research -
per Dragon Magazine 82 "Spells Between The Covers" by Bruce Heard
Level Draining -
Drawing on something that 3E got right, level draining monsters drain stat points. The stat drained varies by monster according to what makes sense. Certain undead may drain points from multiple abilities with a single attack.
Poisons, toxins & venoms handled per Dragon Magazine 81 "Taking The Sting Out of Poison" by Chris Landsea. Poison types assigned to venomous creatures as well in a way that makes sense.
Unearthed Arcana -
Using some stuff, disregarding others. Barbarian class is out the window. Paladins are set up differently in the world so the whole paladin as a subclass of cavalier is out. Cavaliers will be playable, but I'm going with the original version from Dragon Magazine 72