Are your windows large enough to safely use as a fire escape?

yes they are

Hire a good interior designer to create the design for you and to write the specifications for the contractor to look at to price. Investing in a proper design separates you from the mass of tire kickers out there as a serious prospect.

Have an appropriate budget worked out for your want list also. No one enjoys giving sticker shock to people and never hearing from them again because they thought that they could get a theater room, bathroom, kitchen, office, guest room, and a pool table area for under 120K.

Draft plan shown. Keep a small hallway that the bath and office can enter from for privacy and noise control.