The above has highlighted a few things to me. I'm assuming this is your first marathon? It's mine also but I do like to plan ahead so I've practised hydration, know where the gel and lucozade stops are and even got a mate a mile 8 to give me some gels!
This sunday, I suggest you run in EXACTLY what you intend to wear. I did this last weekend with my 16 miler all at MP (I needed to see if I could do it!). Anyway, vest v cotton t-shirt is a whole new ball game on the nipple area! Having applied vaseline pre-run, I came home with blood and cut nipples as the vest is nylon (running for Royal Marsden). I now know I need to plaster them this Sunday and practice again...
It's just little things like that that will annoy you on the day if you haven't practiced. Also a vest is annoying for the first few miles as it bounces until it gets soaked in sweat. Might not annoy you but it was good to know....
I'd also have a look at the Virgin Marathon interactive map so you know where the gel / lucozade stations are. There are only 2 gel points at mile 14 and mile 21. Personally, I'll be having a gel at 8 miles, 14 miles, 18 miles and 21 miles.
Finally, a mate of mine who runs Berlin every year said make sure you keep some toilet roll on you. It won't be pretty if you're caught short and the portaloo has run out...!!!
This seems alot to me. I'm aiming sub 4 and will be doing 10 miles maximum this Sunday and probably 7 miles tomorrow (4 miles easy and 3 miles @ fast pace).
Above you're doing 33 miles in 5 days....that seems lot to me at this stage plus a weights session.
If you're worried about losing fitness, you shouldn't be. I'm running just twice a week and ran 16 miles last Sunday in 2.20. I'd start to back off. Knock at least one of those treadmill sessions on the head - have a light swim instead or just sit in the Sauna! Note, don't sit in the Sauna too much next week when you want to be hydrating!