Besides the design and the plan this bloke will fall down when it comes to talking to plumbers.
He has no previous history and doesnt know a PRV from a TRV and has a right attitude towards other people.
I will place a £500 bet that I am a larger business then him in 5 years as I have actual experience of plumbing, am starting to build up trade contacts, am learning how to charge the right prices and how to invoice proffesionally. what has he got? a great idea with a well written business plan.
And to the OP, most plumbers who rely on word of mouth are so good that they dont need to advertise as constantly busy and do not want to have 3-4 people running around for them. not everyone wants to dream big!
I dont take the mick out of people in mcdonalds so why have you got an atitude towards the one man band. the world needs all sorts of people not just large companies.
And finally you remind me of my brother, he has a degree in "business studies" but has no proffession or trade. What's the point of learning to run a business if you dont have a business to start?