I'll eat just about anything when running - generally "real food", little and often is the key, approx 300 calories/hour works for me - split into 100 cals / 20 mins or 150 cals / 30 mins, That's a gel, couple of Jaffa Cakes, mini pork pie, handful of peanut M&Ms, half a flapjack etc - you get the idea!
Valencia is good, as is Palma and Lanzarote isn't too bad... All cheap to get to and very UK-friendly. there's usually a Valencia & Palma thread in the events forum, In 2012 I met up with a few of the forumites for drinks in Valencia afterwards....
Kinesiology tape - have a look at this link, it's what I used when leaning to tape my feet. I've modified it a bit, but it's a great starting point... Gehwol foot cream is awesome too, get it from Amazon
I use Injinji Trail 2.0 toe socks, love them - Traviss suggests covering them with another pair of socks which might work for you. You can then remove the second pair if/as your feet swell later in the event. Not something I've ever needed to do - but I've never carried 75% of my body weight for 100 miles
You might want to investigate taping your feet if blisters are a problem. I've always taped my feet for anything over 50 miles, (I also use Injinji socks). You need to practice and work out the best strategy for you. There's a few good articles out in internetland and the book "Fixing Your Feet" might be worth getting - or at least look at the website of the same name.
A 5kg backpack for 30 hours destroyed my back so good luck, rather you than me...
The course will be well marked... I had problems with the gpx file too and had to run it through the converter at gpsies.com to get it onto my Fenix.
I ran the marathon route yesterday and it's dry and firm up in the Brecons at the moment, really nice underfoot and even the infamous "Bog of Doom" before the Corn Du ridge is pretty decent, (you'll still get wet feet)
Having said all that - if the MCN team turn the weather machine up to 11 that will probably all change