As far as the money goes, I'm going to have to have enough in the bank for lodging and food, so I'll have a print-out from my bank (so long as that will be sufficient), plus I'll bring some cash with me (do I need to change it before I come? I believe there may be a place at the Memphis airport where I can have that done, if need be.)
I do have to find out now about how my Visa check card will work (extra fees?) and if my Sprint phone will be of any use for me, but that's not probably something I can find out here.
If you are coming for a short term visit, I hate to say it, but being over prepared might not be a good thing. If you are an American, this is likely what will happen... On the plane you will receive a landing card, the landing card will ask you where you are staying and what is the purpose of your visit, the number of your flight. Then you will get into the Non-EU Passport Holder Queue. The IO will rifle through your passport, looking for any landing stamps...
IO>What is the purpose of your visit?
You> Visiting some friends...
IO> How long to you plan to stay?
You> 14 days
IO> Where will you be staying
You> At a hotel / with friends (whichever applies)
IO> Ok, thank you... *STAMP* *STAMP*
If you are really worried, you can print out the stuff you are talking about, but don't offer it unless asked. Again, the more you like you are trying to hide something by being over prepared, the more they might want to question you. Now nothing is going to happen with you other then the IO asking questions, and if they do get curious, they may start asking more questions, want to look through your luggage, etc... They will find out you are a normal person and be on your way.
As far as money, again, bringing little Cash and using your Debit card is MUCH better idea. You are going to get raked over the coals when you exchange your cash. Also, no worried about doing so until you are in the UK. There are plenty of exchange places and they are going to have a lot more British Pounds then Memphis will. Because you seem to be a cautious person, I would give you bank a call to let them know you are traveling overseas and planning on using your debit card. That way they won't accidentally lock your account thinking that your card has been stolen. Most banks won't do this, but sometimes automatic fraud prevention things might click in.
Your Sprint phone will not work in the UK. The only ones that will roam, and only if you call ahead of time to arrange international roaming, are GSM based networks, which are Cingular and T-Mobile. There is nothing wrong with brining it though.