Feelingforty, the general rule of thumb when buying a tent is to add 2 to the number of people you plan sleeping in it, hence why you have been recommended to get a 6 man.
A 'man' size is the width of a standard air mat (pretty much the width of you in a sleeping bag plus a few extra cms on each side, it is not the size of a single bed I've made that error in my head when starting out.
Saying all that, there are 4 of us and we sleep in a 4 man, and we all fit perfectly, there is not much space on either side of the mats but then atm we all like snuggling up together in a big lump.
If you want to go for a double I'm pretty sure outwell did double self inflating mats last year.
With this buying kit malarkey there are ALWAYS pros and cons to everything, so if you want a lovely big tent to camp in then the down sides will be pack size and weight, and length of time to pitch and strike.
Have you seen any of these tents in the flesh yet? I strongly recommend a mooch around a camping store, so you can see what you are getting for your money.
The other thing to consider is what you are getting for your money. There is probably a good reason that the Kampa is a bit cheaper than the Outwell, and that is most likely to be quality.
If you want to become a giant camping nerd go and have a feel of the quality of the fabric the tent is made out of, look at the zips, zips the zips, zip the zips some more until a bloke from the store comes over and gives you a special look, how many guys does the tent have (the more the better) what are the poles made out of? If you plan on camping in the UK you want to get the most waterproof, strongest and most wind resistant tent your budget can stretch to (imo)
I second flutterbye's advice, borrow as much stuff as possible, or go for a w/e camp with some frinds and share their stuff, then you can see before you buy and go and check out other campers set ups too.
re black out material - what about those eye mask jobbies they give you on a plane?
re tables, we used one for several years that we got in Aldi - wait a few months and they start selling basic camping kit at very reasonable prices.