I really don't see an issue with the rooflines. Looks like the angles are fairly similar and the clean lines of both structures should be easy to coordinate, especially in your open, rural setting. Since you've found a stunning deal, I would say, go for it! I definitely would want to find an architect ASAP and by all means, before you pour the slab, make sure you have a plan to coordinate.

I could see doing something like French doors with opaque glass so the lite could come thru to the rest of the house. Also double French doors would allow you to open the area up completely whilst doing laundry. You could even leave everything where it is (dryer) and build some storage on the left side. I would image the sink would be very useful - I'd be lost without mine in the laundry room.

It depends on the species of wood (I.e. How hard or soft) and whether or not the ambient temperature can remain as stable as possible. What you caulk and paint in warmer weather may look great now, but when it begins to get colder, the wood begins to shrink, and the caulk will begin to pull away. This will look worse than if you didn't caulk at all. My suggestion is to use a caulk like the brand called "Big Stretch " in an attempt to avoid this.

I love the general concept of beams and adding beams, but in this space with the ceiling as it is in the drawing, I think adding beams at lower levels makes things too busy architecturally, considering the soffitt and all of the other planes, angles, and openings.