In what country are you building this house? 9 foot or vaulted ceilings are taller than the US builder average of only 8 feet (this is the distance from the ground to the ceiling). If you have a small room, having a higher ceiling (even only 1 foot extra) will make the room feel more open and airy. In a small house of 1500 square feet, having high ceilings would go a long way in making it feel much larger than it really is. It is especially beneficial in a hot climate because heat rises so you will spend less on cooling costs. It is not so beneficial in a cold climate. It still looks nice, though!

From this photo, it's hard to tell exactly what's going on. Is that a porch? Is this an apartment? Two story house? Need a wider photo and one at an angle to see just how the house is constructed. This is all possible (Anythingis possible with enough $$!) You should consult some experts for costs and design ideas.

For the living room, the focus should be the balcony area. So flipping the couch to face the wall and not the dining table will help. Kind of like this pic. Even if you already have the sectional that is in the diagram, you should be able to flip it. In fact a sectional would probably work better than the couch in this pic. I also really don't like the style of this pic, but it showed what I meant, For the girls' room: No matter which bedroom you choose, you should maximize floor space so that they have the biggest play space possible in their room (as they get older you can add desks for school work and such). To get this space, I would give them bunk beds. This configuration gives them an open feel and more storage, essential for girls. You posted two different kitchen designs. This makes it hard to give you advice. I agree with other posts that your sink should be away from the wall. This allows you to have stuff to the left of you (drying dishes in my house), while you wash vegetables on the right of the sink. You need the same space on both sides of the stove, also. At least 24 inches on both sides is good. 36 is better, though. The first design has a nice little countertop space that adds a place for your daughters a space to sit a watch/ talk to you while you're in the kitchen. When they added this to the first design, you lost cabinets on the other wall. This is bad, as the space is already storage limited. Try making the rounded countertop bump out into the living space more. If you play with the shape, you could make it work without losing the cabinets on the other side. It doesn't have to be rectangular or a perfect circle. You can see how this one isn't confined to the floor plan of the kitchen. I think this is what you would need to do to make it the most functional.

Going with professional has its own advantages. Afterall he is pro, so he has studied more and has more experience. However is this person from the kitchen shoppee, which is giving you quotation of kitchen installation? In such cases, I have experienced that they just make boxy kitchens where they add lotsa fittings, that increases your budget. Open shelves does not need such fittings, so such are omitted...Normal door wali cabinets are less and number of drawers increased. Going on own is not a bad idea, provided you need to study it well. Note down the requirements, classify work areas and so on... In this approach , you have to go bit slower and carefully. Allow some flexibility in design, so that in future , you can alter as per the need. Sometimes we come to know the problems after few months/ years and we cant change it later. Ultimately compare between [your time+ efforts+ study+ error chances] Vs Hiring professional and go ahead accordingly.