Overall it's a pretty easy process. Getting the front cutaway to look good is my biggest challenge. If you have to dodge the lower buttonhole (i.e. cut to outer side of it) the angle can look too abrupt. I posted an example recently here where I think my cutaway is too sharply angled.

Shortening the sleeves slightly should not be an issue until it gets to those sleeve buttons -- then you have to start moving buttons to maintain the distance from lowest button to sleeve hem. The jacket I link to has fake buttonholes under the sleeve buttons, which would further complicate the matter.

It's a lovely jacket and I hope it comes out well for you!