Is this design of a wholly new house or redesign of an existing old 3,200 sq ft house ?
If it's redesign then why do you say that you have got PP for a 1 off rural house ?
Redesign within existing form ought not require PP, surely . . . .
Also I see paradox between wanting to (re)design 3,200 sq ft imaginatively and still claiming that money is tight.
If you're badly off just give it all a good lick of paint, throw out carpets, sand & varnish floors, some new windows + doors and new trimmings.