Site sponsors are companies up in the top right of the website.
I am actually on gumtree right now looking fridges to get myself back up and brewing again.
If you can, get a decent tap. You might be able to get a great second-hand tap like a Perlick 525ss as newer models with flow retrictors etc come out.
I am a fan of owning gas outright. You could look into the extinguisher thing, but I can't comment on it.
You will want a long shank to go through the fridge insulation.
I am a big fan of the FFL/MFL threaded pushfit adaptors, I am sure you can get no-name ones from ebay cheap if you know your exact line diameter. I got JG ones, but they are expensive.
I regret not setting up more elegant lines in my last setup, so this time I am going to plan it so that it is nicer to use. I also regret using the cheap chrome/brass hosetails on my shank, they corroded. At least my diet was high in essential chromium, copper and zinc. This time I will use an elbow on the back of the shank so I can tuck my coiled lines somewhere less obstructive. I probably left the fridge slightly open a few times because beer lines were pushing it back open.