Yessss. A wonderful choice.
For his top, the easiest thing I can recommend if you're not looking to buy patterns is to get a shirt and take a pattern off that. Find one that fits comfortably and pin it into a new shape. You can easily fit a zipper up the front thanks to the seams in the artwork (even if it is questionable in the game's canon to have a zipper!), and lengthen the front and back to have the pointed and rounded effect his shirt has. Jackets are also an option, but I've always seen it as a resized shirt, mainly for the shape and fit whereas jackets aren't normally so fitted around the waist.
If you're concerned the shape isn't right, look at slim fit shirts. Normal shirts can be quite baggy/generic, whereas slim fit ones are tailored to fit a man's waist and hip area. You should be able to get a pattern for one, if not, you can usually pick one up with good fitting from about £8+ in most supermarkets (which is about the same price you'd pay for a good pattern)!
The sleeves just need widening at the top. Attach elastic to fit your arm into the inside where the red band fits and they should fit easily with a nice flare at the top, without showing off any mess!
Also seconding fabric choices - thin cotton won't hang correctly, but if you get a nice cotton drill or even a suiting it should hang correctly. I'm in the middle of remaking my Vyse using cotton drill and lining it, so it has a good weight to it and won't budge.
Good luck with it! Can't wait to see it - I love seeing SoA costumes
