Wow Lowena you certainly are getting ahead with your plans.
I have a Horn Cabinet, which I absolutely love, and is slightly different to the norm, mine opens up to the back and thus gives an enormous work space - Whilst several years old now it is called the Sewmate 2. This cabinet when not in use can be folded down and put back against a wall, but in order for the top to open it has to be pulled away from the wall, and there is a fold away support at the back which has to be opened to support the top flap.
I love the fact that you can work on huge pieces of fabric - think wedding dresses, curtains here and with the sewing machine on its platform in the lower position the fabric slides through the machine and continues onto the table top so there is no drag. I also much prefer sewing with the machine in its lower sewing position, i.e. with the plexi around the machine - it is amazing not to have the drag of the fabric falling off and pulling against you. I also have a separate Horn Cutting out Table, and find that this is so useful especially when cutting out as it is higher than my dining room table. This table folds down when not in use and has two useful cupboards, it is also on castors so can be moved around easily.
Something else to think about with a Horn Cabinet, is the way the doors open, on mine the main door that opens with the machine immediately behind this, has caddies on the door, now if this was the other way around any fabric you have could catch and snag on the open door's caddies - I think you really need to get hold of a Horn leaflet and then you will see what I mean.
Why not get in touch with David, Jason or Angela at Horn in Swindon and they will send you a leaflet of the current range - I have always found them to be extremely helpful phone no. 01793 834304.
Good luck with your plans, how lovely to be able to plan ahead and get your new sewing room just how you want this to be.