I have tried a gazillion different solutions and was amazed at the difference, so for me this is an absolute MUST. You wouldn't think there could be such a variation, but believe me, there is!
I've tried Fake Bake, Fantasy Tan, NaturaSun, Tantrick, SuDo, Solglo, California Tan, Bali Sun, Sweet Illusions and Ocean.
So far my favourite is California Tan (although their bottle size is a pain) and I'm quite pleased with Ocean. NaturaSun lasted very well but was a little perfumey. Tantrick I personally didn't like but I can't fault their customer service.
Some solutions have a good tan but an appalling smell, or bad guide colour, or take forever to dry. It is trial and error so I would certainly recommend getting as many samples as you can and trying them out. It's also suprising how they will react on different people and how different people 'wear' more quickly in certain areas, so be sure to have 2 or 3 models (I use me, my mum and my sister).
I would go for a brand that does at least a medium and a dark colour, although I don't see the point in some brands that do about 10 different solutions, you're never going to use them all!
I have a pop up cubicle which I would recommend, I would also say get the bronze version if you can, not the black - it is suprising how much lighter it is inside. Another good idea is to get a clip on daylight lamp or two for lighting (a trick picked up at the Spray Tan Cubicle stand at Earl's Court).
As far as machines go, you will need to know how much you will be spraying. I use the Nuress system which has been fine so far - very light and easy to use, easy to pack up and carry, but I don't know what its life would be for constant use. I have heard the Mini Mist machine is very good and I know the Spray Tan Cubicle co sell this, as well as a Nuress kit. I would go for an HVLP system or a compressor with an airgun, not an airbrush - that is my personal opinion but I think they are much quicker and a bit more '***** proof' than an airbrush.