Hi
You seem to have so many questions but I think your one solution is your local planning office, from my own experience they will give you the best advice. Sometimes it may not be what you want to hear , but they will put you in the right direction. When you have got this sorted out you will then enter the world of ever changing building regulations.
I built my own house 10 years ago and my main advice to people is to talk as much as possible to self builders, and hire local contractors from recommendations only and if possible avoid yellow pages. Walk round builders suppliers yards and look at plenty of self build magazines to see what is available.
Don't be put off by TV programmes which tell you to always have the services of a on-sight architect and sight manager that is just an unnecessary expence, if you get a good builder he will more or less give you all the advice you need. But above all remain friends with your planning office.
Good Luck
William