Hello. I think, that the best way to make Geralt is cipher. He have native huge damage boost 40%, can effectively fight both melee and ranged, and have a various abilities many of them very similar with Wither magic. About stats, i suggest focus on Might for additional damage, Dexterity for quick casts and Resolve for concentration and less interrupts in a fight. So, stats may be:
M 16
C 10
D 15
P 12
I 10
R 15
Two great swords + arbalest (like in Witcher 3), and very handy for opening fights.
About abilities:
Axii - lvl 1 Whisper of Treason and rwo other powers on lvl3 and 5
Aard - level 1 power Mind Wave and lvl 2 Amplified Thrust
Quen - lvl 2 Psychovampiric Shield (drain int from enemies, increase deflection) and especcialy lvl 4 Pain Block - gives additional DR and restores stamina, just like original Witcher spell, as i remember.
Yrden - its hard to reply, bun i think lvl 2 Mental Binding works the similar way - AOE paralizes target + nearby enemies get Stuck. Or lvl 4 Silent Scream - Stun target + deals AOE raw damage to enemies.
Igni - its hardest to reply with native cipher powers, so it might be scrolls, as you already suggested - Fan of Flames and Ray of Fire.
As for armour, yes it might be scale or leather armor.