As has been said already, you need a phone line. I would suggest getting hold of BT Retail and getting that on order ASAP as that is going to take some days to get installed. Don't be sucked into the push they will give you for BT Broadband, unless that is where you want to go. You don't have to buy both at the same time or from the same people (I have ranted about this in another thread, so I won't repeat myself).
I wouldn't bother trying a simultaneous provide (When BT turn the DSL on at the same time as install the phone line) either, in the numerous I have done, less than 0.5% have worked and end up taking longer to sort out than ordering it after the line is installed
I would suggest that you don't go down the LLU route as once you are there it is more difficult to move. Taking service from a BT Wholesale provider will allow you to move between more ISPs more seamlessly if you find that the one you pick doesn't do all that you want (I hope this isn't the case but you don't have huge amounts of time for research!) and if you are earning a living from the connection, I would suggest that you pay for expediting the ADSL once the phone line is installed. This will cost you £165 but will get you online 24 - 36 hours after you place the order (Depending on the time of day you place the order and BT's database having been updated following the new line install) as opposed to 7 days.
Reading this through, I seem to have a load of don'ts so to summarise with some do's:
Order your phone line ASAP
While you are waiting, pick an ISP (I suggest a BT Wholesale based product, particularly as your bandwidth isn't huge)
When you have your new phone number, expedite the ADSL order
Play poker (And win!)
As for IP space, we can do static blocks in either IPv4 or IPv6 but I suspect that's getting a little too technical. You guys want to play poker and make your living, not play Internet
Feel free to give me a shout if you need a hand (Sorry, couldn't resist the pun