Finished coat / thinking about the next one

So I've finished – I'm quite happy, I am half contemplating opening up the sleeve lining and taking out some wadding, and I wonder if I may have messed up the tacking of the vent as the opening seems to be pretty asymmetrical (as Rory noted before I should think it's mainly a balance issue). Happy with the chest though, pressing it made a good difference too.

I seem to have a bit of a stain on the front. No idea what it's from – definitely going to blame a flatmate. Any tips for removing it?

I'm now also thinking about my next project. I was thinking of doing something in linen just because I really like linen jackets, but I'm guessing this could be much more challenging – would this be too much of a step up for a beginner like me?

Thanks!