Morrowind esque
My experience with Elder Scrolls 3: Morrowind was my favorite. The ability to craft spell components was amazing. I found code on uesp.net for the maths. I created a spreadsheet and modified it to dial it down to 3 stats. Math creates a DC to beat with a d100 roll. For physically focused characters, there is math for mix and match armor pieces.
Don't worry about the math, I'll make the necessary calculations and apply the results to your character sheet.
Since this is essentially alpha test of my modified system, I will utilize the side quests and faction quests in an open world Morrowind without the main quest line for multi-player facility.