Is it correct that these are "decorative only" beams, and serve no structural function? If so, then ask your builder to give you architectural elevation drawings of the space both ways. Then see what you think. I also recommend that you find a copy of the book by Architect Sara Susanka called the not so big house. I say that because there are a lot of contemporary and well designed homes in the book. You can see what you think when you see them. Her book also discusses how spaces that are too large can feel as though they are too formal and lack intimacy. Since it sounds like you don't want to be too formal, I think you would get a lot out of this book.

I like the warmth that the beams add. but truly it needs to make sense . im not do sure a beam would start off the half wall . layout of furniture is hard with a limited floorplan .. maybe take a layout to a desgner .. for furniture and beam placement . it would be worth the consult in the long run! good luck!!

It shouldn't matter much if you install the necessary blocking for the future false beams. It would help if you posted a detail showing the size and material of it and how it will be supproted and trimmed. Obviously it would be easier to install the beams before the cabinets and finishes.

To illustrate in more detail of what "making it look like actual structure" means, having the beams (rafters) disect a window or opening, or compete with soffits is usually a bad look and calls attention to it's 'fauxness.' In your case, you have the 2 windows, the inset cove, the entry area, and don't know what's on the other side of room. Here I just tried to count equal truss spaces in a pattern that avoided the windows and stuff, I hope you get the idea and can find a spacing that works to look like real structure and also has proportionate spacing in relation to the overall feel of the space and ceiling height.