You will need an architect

The only real option I see is to make your walkout basement your main floor, and make the new entrance in the expansion. You could also sell this and buy something that fits you now.

Keep the add on to the ground floor so the original home stays intact.

Or have a little wooden bridge at the second floor level and add a second building, which would maybe have just bedrooms. Would keep the feel and let you do more in a second smaller tower.

You have 750 square feet. A 2 bedroom, one bath, large kitchen addition could be 400-500 square feet. Take some time to learn google sketchup. Then talk to an architect or design-build firm. Make sure you hire someone who works most of the time in your budget range, not someone who is going to decide this tower house is a sky's the limit project. Unless, of course, the sky is the limit.

The least expensive way to add on is to do so at ground level, which may be up at the second floor height toward the back where the hill rises. Your ideabook already shows lots of ideas along those lines.

This is amazing. I am commenting just to get notifications on updates.

Wow that home is fantastic! It appears to be self sufficient as well. Would it make sense to attempt to erect another tower next to it and have a balcony connecting them? It may costs a bit but with the desired rooms your creating you may have to make another building. 2 bedrooms, 1 bath and one kitchen right? What are you estimating for costs and additional square feet added?

Absolutely love your tibetan prayer flags! What a fantastic home.

I have run through so many options, talked to my builder, even worked with architect for a bit but it made me realize I am not going to be content until I find the right designer type who can present some ideas on how to incorporate the existing space (renovation) into the flow of an addition. I appreciate all the comments so far. For your info, it is completely off grid - so in addition to being on sloped land and being a tower, we will also have deal with expanding/redesigning placement of rainwater catchment and storage, septic etc..

Nice work :)

But now you have gutter issues....

Yes, what happened there ??

still off grid? do you harvest rainwater from the new roof?
congratulations on your solutions. best wishes.