Yes it is. Whether you want to just replace one or two windows with a hup! wall or add hup! to existing walls to create a completely new look, hup! can easily cope.  You can choose between having a cill between the dwarf wall and the hup! wall and having a different wall finishes on the hup! or you can choose the full cladding option where the wall finish can run the entire height of the building for a more premium look. hup! works on both 250mm and 300m walls -the width of the existing wall must be specified at the time of order. If Building Regulations are required, you will need to bring the entire wall to 0.18 UValue. 

You have 50mm to play with including the insulation and floor finish. Using a threshold this could be increased to 70mm, but the height of any existing internal doors would need to be considered. There are many floor insulation options on the market.
For Tiles you can choose Pro-Warm Tile backer which is available in 6mm (U-value 5.5W/m2K), 10mm(U-value 2.62W/m2K), 12.5mm or 20mm(U-value 1.65W/m2K) and 30mm U-value 1.1W/m2K). 
For other floors Eco-tec floor foam is only 6mm thick, or if you can use a threshold and want to be Building Regulation compliant you could use two Kingspan products. 
Kingspan TF70 which has a U-value of 0.55W/m2K (insulation only) and is 40mm thick +18mm chipboard. Any floor finish would need to be less than 12mm, to come in less than 70mm. 
Kingspan Optim R 20mm which has a u-value of 0.25W/m2K as a floating floor which can be used with a floating floor like laminate or used with a Fermacell 15mm board to adhere other finishes to. 

The sound will depend on the claddings chosen and the make up of the brick wall it is being compared with. If finished with render or brick slips, there will be very little difference vs a brick wall as the calcium silicate board does a great job of breaking up the sound.

Yes - many hups are built with bathrooms. 

Yes, this is possible. However, if you are extending the base, you will most likely need a Building Regulation approval (only conservatories below 30m2 are exempt). To comply with Building Regulations, the existing base may need to be insulated. Any extension to the base will need to comply with Building Regulations and some underpinning of the existing base may be required. You will need to consult with your Building Regulations Approver before commencing basework.