Is it possible for a downstairs toilet to be installed into cupboard.

Yes its possible, providing you can get water to the toilet and the waste is taken from the property to meet regulations. Unless a saniflo is fitted instead again waste has to be taken to the soil stack in the correct manner this is an easier option if underground waste is hard to get to!!!! And also there is the cost factor as well it can be very expensive

Yes this is possible, depending on the location of the waste and inlet to the cistern. I wouldn't recommend a saniflo, they are full of problems and costly to maintain. Hope all goes well. Thank you

Waste is the most important, as long as you have a timber floor you can usually get a hot and cold supply to the area needed. As suggested before I would stay away from a saniflow.

Site survey would need to be carried out to ascertain drainage layout of property,water supply options and extraction fan position, building regs would be advised for future sale of property.