To convert a commercial property into residential you firstly have to get a change of use from the planning department to say that they agree to the property being made into residential property. You should also check that there is no prohibition in the title deeds. Then to do the actual conversion you would need a building warrant again from the council. Finally if you want to use it for HMO you would need an HMO licence as you know. I hope that helps. Happy to discuss. Please leave a positive rating so that I am credited for my time. I suggest you discuss your plans with the planning officer local to the property to get an informal view of whether your proposal would be acceptable to them and the existing planning policy for the area.