I don't think you're being over-optimistic at all.
1) IMO, if you've run that distance, you can probably run 26.2 no problem. In some marathon training plans that's not much short of the longest run before race day.
2/3) Yes, I have a vest and I used it yesterday to carry water, a bit of food (more than I'd normally need), facemask (for post-run McD's), mobile charging unit and cables (had to run the VLM app and I wasn't sure how it would affect phone battery life). I normally would only take water and food, normally just water if it's an organised trail marathon, because the aid stations are normally fabulously stocked. The vests are so comfortable too, but if you didn't want to go down that route then yes, run via the shops along the coast. There's talk of a Pier 2 Pier run involving (I think) Bognor to Brighton and there are plenty of places along there. Or get a support crew to drop the odd bottle with you or something (loads of runners yesterday had people helping them).
4) My legs were a bit of a mess before I started yesterday after being on my hands and knees all day Saturday insulating the loft. But when you're out there, you just get through it and actually it eases off after a while. But yes, I took it easy last week (fewer miles at a slower pace) and I was back out this morning to keep my own streak going.
The most important thing is you have to WANT to run a marathon. It's a hell of a long way if you're hating it the whole way round. Had this conversation with a mate yesterday, who ran the last mile with me – what is the point of running (or any form of sport/exercise/activity) if you don't enjoy it? Waste of time and you end up feeling worse than you did before you started!
Finally – and I know [MENTION=27279]dazzer6666[/MENTION] would agree, but many others might not – I would always favour trails over road. Especially if you're legs are feeling it because, honestly, mine feel fine today. It could be that we organise (or resurrect) the NSC marathon and get a few of us (up to six, I guess?) involved. I'm sure people could carry some food and water for you Actually, I think – if you did the route I did yesterday – there would be enough places to stop along the way, maybe?
Agree 100%. [MENTION=6886]Bozza[/MENTION] your training volume would easily allow you to have a bash at a marathon......whether it’s trail or road doesn’t matter but as [MENTION=24635]Greg Bobkin[/MENTION] says you’ll find trail so much easier to recover from (it’ll just be a slower time obviously). As regards hydration etc, would be useful to try out a few things on some of your longer runs in advance, and you definitely shouldn’t attempt a marathon without water plans. As well as the shopping en route option, if you don’t want to carry you can also pop out beforehand and place a few bottles at strategic points. There are also multiple taps on the SDW (for example Upper Beeding, Truleigh YHA, Housedean Farm layby, Southease Church, Southease YHA etc etc) so any long route on there isn’t going to be a problem. Ditchling Beacon car park usually has a coffee van or ice cream van there.
I’m still off anything long distance atm (4 months now) with a persistent ankle/heel issue (legacy of a sprain) but once I can get back up to comfy 3hr+ jogs (currently at about 2 max) I’d be up for an NSC marathon