Don't forget your home insurance may not cover you should your house burn down due to you having a 10kw shower on <1mm bell wire etc so get someone in to give some advice and the main thing will be that they can tell you what to do and how to do it and so long as you don't plaster over the wiring/stick laminate over the floorboards etc so he can have a look and say "that looks fine to me" you're sorted as he'll willingly sign off the job as its basically the same as if he'd got a trainee to do the job but not have to pay them