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 understand going with the grey since it is an 80's style house. You could also do bright bold colors. I do not know if that is your style. I have attached a quick rendering of the gray scheme you mentioned. I prefer light colors above dark colors. This keeps in theme with the sky and earth. Makes the house seem more grounded. The dark entry also draws your eye to it especially with the light coming from the other side of the house. I have also attached a quick rendering of a blue scheme. It looks like you are on a beach and I thought this would blend in with the surroundings. If that is what you are seeking. Hope this helps.

I haqve just seen this , and it is well over a year old , so presumably you are well into renovations , or maybe finished . Here's my take though -- probably too late though ! Your picture looks like those 70's photo's that faded and yellowed ( sorry to be rude ) . So freshen and modernise . Paint the walls white -- not beige or yellow . It will look so much 'cleaner' . redo the dark uprights and base boards -- I can't tell if they are dark green , or black , but I'd do black stain over it . The fence I would also do in black . The yard , step one , would be hide and soften it . The Cape Cod chair paint in white , with the pailings in bright primary colours -- each one different . Add 2 or 3 planters -- different shapes and sizes and heights , but all stained a nice Kwila brown or charcoal or similar . Big leafy plants , cactuses , yukkas , maybe white and light brown pebbles , marigolds , colour , texture , different height plants . Personally , I would go further -- paint the roof , rip up most of the pavers , possibly even change the windows to bronze or charcoal frames . Just some quick ideas from an experienced amateur haha .

Led lighting running on both sides of each of the beams - you can buy it in strips. I would go for a bright white but you can even get it in colours and or changing colours. I would also do the same along the floor under the cabinets and perhaps between the upper cabinets and bench top.