I use long training runs to experiment with food to see what I get on with and what I don't, everyone is different in this respect. In longer ultras where i'm going to be running for 8+ hours I eat from the off. Tend to start off with food like sandwiches and pork pies for the first 8 hours then switch to sweeter stuff for later, this strategy saw me comfortably through a 100 miler recently. I believe I read somewhere that fat and protein take longer to digest so it takes a while for foods containing these to work their magic. There, that's my input and enjoy the food experimentation.
Slow and steady is the way Stu. The guy that won TR24 this year had very similar lap times from 1st lap to the last!
Fuelling is a bit of an individual thing and over 12 hours should not be a problem. A lot of ultra runners will eat 'proper food' on long races ie not use gels etc. personally I have a diet of ham & cheese sandwiches, cold pizza, pork pies, cakes, sweets & crisps on long races. You can eat these on the walking breaks you will inevitably take.
Also don't neglect electrolytes. Resting...one thing I would do is make sure is you don't sit down but take your breaks standing.