To get all your tools and a van and everything it depends on how much you shop around for a bargain but making sure its quality, for advice on tools there's actually a section of threads for it.
There's actually a thread about buying a van that was started recently so that could be worth a read. As for the fully qualified it really depends on qualified for what, there are loads of different qualifications you can get, there's oil, gas, unvented systems etc.
Training will cost you, unless you qualify for a free or subsidised evening college course, the intensive courses by all accounts aren't great, but then a course alone isn't all that great, practical work all takes place in a workshop environment where you don't come across the boxed in pipe work, the seized compression nuts, gate valves that snap when you go to turn them etc. You need to be out there getting some experience working with a plumber who can guide you through these problems, and at the moment it's hard to find people who will take you on.
The best advertising you can do is just going round the local area putting leaflets through letterboxes and introducing yourself but not pushing any work on people, also recommendations are always good, if you do a good job for someone they'll tell their friends/family.
Best of luck with getting set up,
Sam.