Technical drawing

Craft, design and Technology(CDT)

These would help,

coming up with the ideas is good, but if you can’t draw them accurate, neither your clients or workers will understrand, so technical drawing is useful;

also building some things yourself will save costs, knowledge of basic woodwork and metalwork would be good.

you could also take college courses in Electronics and perhaps plumbing. Still get the experts in if you have to, since if you are doing major alterations, a professional may have to sign off on a job for insurance and legal purposes.

knowing how things work will help at the design stage

some colleges run courses in Interior Design.

Good Luck