Hello, I haven't been to Watford but it looks like you're quite well served for vape shops. It's worth going to a shop for your first purchase at least because you can ask to try different things, they can show you how to set it up and you can take it back for help if you are having problems.
This store looks like it has a good product range. They have a store at 17 Harwoods Road.
You've also got a Totally Wicked at 322 St Albans Road. TW are a chain who sell rebranded stuff at a markup but they are geared to newbies and carry a good range.
I tried in 2013 with a rubbish kit and it didn't work. Now been 2 weeks cig free. I started with a Kanger emow mega kit which worked. However I have new shiny stuff that came today and holy shit, the taste difference is insane! I got an eleaf I stick 40w as the battery and for the tank a nautilus mini. Ordered online but you can get them from shops, I wish I had got this to start with