I'm thinking this could be fun to play, because Letho is a giant (or a mountain of meat, as Geralt would put it), but an assassin, breaking stereotypes.
Only venture I can think of is DB. CW can go either way and being LDB is a route in itself. Other than that not much else, unfortunately.
*I made a Triss Merigold for this game, although her options were limited... curious if anyone made a Geralt? I still want to make one for the hell of it.*
What I recall of him is that he's bald....
He uses disguises if he needs to assassinate someone has good acting skill (from geralds journal) and lighting fast reflexes.
Witchers are known to use alchemy so use that in your character somewhat magic and have increased reflexes, speed, strength and enhanced hearing (so turn up your volume to the MAX!)
As for Geralt, still drafting him up.
Unfortunately, I cannot remember if two-handed is really needed (you can if you go legendary on some skills to go over level 81, if need to be). If what you after is accurate, you might want to specialize in alteration as I remember a protection against the Draug (sp?)/ghost battle field scene where I know I needed it (unfortunately forgot the name of the spell off the top of my head ... Axii??? It's been a few months I played the game.
That is one I am thinking of, forgive me. Alteration with some sort of resistance is like Quen. Go for that one.
You can for Savior's Hide, if you are comfortable w/o "pants". Forsworn armor is another and probably leather as well. In fact, iirc, most light armor seems to be pretty much sleeveless, so choose what you think best (costumes are quite different between these games and in fact you can go "armor" for Thalmor clothes, if you can stomach that much [to me it reminds of that Empire in Witcher w/ Cynthia]).