Wow! Go you!! I must say I'm not surprised and could've predicted this was the route you were going to go :-).

I'm thinking of registering for a 50k trail run in June, so I'm all ears for tips too. I've got Big Sur in April so I'll be upping the hill running before that anyway. I've got some trail shoes on my holiday wishlist too.

GOOD LUCK! YOU CAN DO IT!

Can't speak from personal experience here, but my dad is someone who is crazier than you. He runs 50 and 100 mile races pretty regularly. He started with marathons and worked his way to ultras, then to 50's and finally 100's. His training runs are 30-40 miles multiple times a week getting ready for the 100, with rest a week before the actual race. Rest being "small" 10-15 mile runs.
But like I said, he worked up to those. If it were me I'd start with a half, work my way to a full, THEN do an ultra. You want to be able to at least run the distance of your race beforehand, so I don't know if 20-22 miles will be sufficient enough for training. If your race doesn't have a ton of hills then if you only are doing 20-22 miles for training throw hills in with it, lots of hills.
As for shoes, I don't think he uses hoka's for ultras, but I know he uses them for the 50's and 100's. If you haven't heard of them check them out. They look silly and are expensive, but according to him and his fellow 100 mile friends they are a dream for running long distances, they also last forever. Other than those he uses higher end Saucony running shoes for his training and shorter races. He has about six pairs, and each one serves a different purpose. I don't know what all they are, but I know one or two is for trail, and one is for the city (never sidewalk).
Before the race do a carbo load, he always goes to a Chinese buffet or something similar and eats pretty much the whole buffet. Sounds disgusting, but he said it really helps him get through the race without feeling dead. Afterwards he does another carbo load, but not as extreme as the one the night before. He also ices his feet and legs in intervals. For the next week he does a ton of stretches and puts on some compressions leggings to help his muscles recover.
Well hope this helped! My dad is 60 by the way and has done this extreme running for 10 years now.

Relentless Forward Progress was the one I was going to buy!

I read Scott Jurek's book a few months back and loved it (whenever I'm in Boulder I'm secretly hoping I'll run into him, lol...yet to happen, but I can keep wishing!).

I'll have to look into these "Hoka's". Right now I have Brooks Cascadia trail shoes, and they've been great so far.

A coach is a great idea in theory, but I honestly am not sure I could afford it (I know, it's all about priorities). I'll have to think about it though. I was kind of hoping I would find a book to be my unofficial coach...like Hal Higdon is for my marathon training.

If you can't afford coaching I would try to find running groups or crews that meet and run together in your area. There membership fee is a lot less than coaching fees and depending on the group or crew they can offer a lot of support in training and planning in addition to company on long runs and accountability. Plus they can be a lot of fun!