Congratulations, you learn more from failures than success.
New rules, new mechanics, new play concepts, new display of information and a complex dungeon…what can possibly go wrong??? ;-p
I’m a bit agnostic when it comes to game systems until combat starts taking way too long. Except in superhero games.
My only suggestion is try a simple scenario to let everyone get used to combat and their sheets. Soon enough they are just there for occasional reference. Or tracking HP and ammo.
Remember any attempt becomes easier the second time it is tried. (As far as ICRPG rules). Let them try crazy.
Inventory control is part of the game, but you can deep six it for a different method. But 10 items can be enough if they are flexible or broad. Gauntlets give you +2 armor…not just your hands.
If a magic staff only does one thing, for high powered characters, it’s a low end item. It can add to +3 to casting, grant easy rolls on fire spells and store 3 spells in equipped status. Now we are into the high mid tear of items. If playing high fantasy.
Or do something odd and have semi~free form magic and abilities. GM decides the complexity of what they are asking for, 1, or 2 they have what they want, 3 they get part of it. Something they definitely should have, they just get, something they probably should have, roll a d4…something they should probably never be able to do, Percentile. D4 is 50/50 they get it, and 75% they get most of it. D20 is 10%~15%.
Only part I hate is them needing to write it on their character sheet so now they have it when they want it, and or players asking for crazy things for the 3% chance they might get it. But it’s a method to grant starting loot as they need it.