I went to Tenerife in December last year and ran this route, it's about 35 miles total and 14,000' up and down! I didn't get right to the top of Teide as the weather was horrendous - it was a whiteout and very dangerous with snow and ice, you shouldn't have that problem for the race.
tenerife is a trail running paradise, the Anaga mountains and Masca gorge are also worth doing.
As far as the route goes, well - it's 17.5 miles up, then 17.5 miles down! The first 10 miles or-so is through forests, and trails with a bit of road at the start. Then you hit Teide and it gets more barren and volcanic... There's nothing super-steep or technical , it's more of a long, long climb/descent. Your quads will be screaming by the end!
I hiked most of it and it took around 15 hours, but I wasn't pushing the pace and stopping a lot for photos. You go up to 14,000' which if you're not used to altitude will start hurting at around 8,000'
it's fun - though I wouldn't pay to race it, (and I didn't) for around half the price of the 0-4-0 I got a weeks holiday, with car hire, flights, hotel etc... Depends on your motivation for doing an trail like this...
Dank - it depends on the weather, in normal conditions it'll be a bit boggy, grassy, rocky and muddy with a bit of decent trail and road thrown in. If it's wet replace grassy and muddy with boggy
My preference is for a lightweight, fast draining shoe with a rockplate, (the old New Balance MT110 which is now discontinued). I'm loving the New Balance 1210 Leadville at the moment which I'll probably use at Round 1 next weekend. just don't get on with Inov-8 shoes, have tried loads on in vain - they're just too narrow in the forefoot for me.
In my opinion cushioning isn't as important as you're on soft ground for most of it, yes - so there's some rocky sections but it's not Snowdonia or the Lake District and the rocky bits are fairly short lived. A rockplate definitely helps smooth out these sections though.
Maybe not much help? Use what you're comfortable in is the best advice I guess!