Hi Jon,
Thanks for sharing all that - I reckon you'll be typical of any number of members at the moment and they'll be keen to contribute or just watch this discussion!! The only thing I forgot to ask was whether you assume EdT to be your #1 aim for the year - I assume it is given the expense and time commitment in taking part...
Anyway, my thoughts, based on experience, common sense, but no qualification....
Abilities you need to develop/improve/maximise:
1. Ride for 10 hours with no major stop.
Arthur rightly councils you not to get too hung up on this, but the fact remains you need to do some long rides at some point if you don't want the last three hours to be an ordeal. I'd be looking to do 2-3 x 8 hour rides during May/June. If these are not to be too painful then you need to be doing 2-3 x 6 hour rides during March/April. You can guess what I'd say about Jan/Feb..... I'd do these at an intensity which means you're pretty stuffed at the end. I know you are riding in for the Sat cafe run and that sounds like a long ride to me! However, remember that this is more like 2x3 hours with a cafe break in the middle. The cafe makes it much easier! That aside, I'd recommend sticking with these rides as much as possible for the endurance, fat burning, but also you will feed on the enthusiasm of the others. Also teach you to ride efficiently while knocking elbows with other cyclists! Also look at some early season Audaxes like or own 3 Brideges.
2. Ride up hill for an hour at a time.
You've seen what the climbs are like. Its hard to simulate this in the UK unless you fancy going up to the Scottish W Coast for the Bealach na Ba. But what you can do is simulate 1 hour's worth of intense riding. To me this would be a series of 90 min training rides (incl 15 warm up and 15 min warm down). If you can do this every week that would be great. Climbing is all about strength : weight ratio and I'm tempted to quote Robert Millar's mantra of "ride more, eat less"! Sounds best in a scottish accent. Further to get some more intense riding done - how about doing a Sat training ride instead of the cafe run every other week?
3. Tolerate 30oC heat.
Don't think there's, realistically, that much you can do other than have a really good hydration strategy on the day.
Fitting all the riding in. This is the challenge! I'd avoid back to back hard days so if you riding on Sat, then I'd invest Sunday on catching up with the rest of your life! I'd then be looking on getting two sessions in during the week. How about one 90 min ride plus something else. At this stage of the year it doesn't even have to be riding. Swimming? I'm told there's a good spin class at Abbey Leisure. But certainly when the clocks change you should be trying to get out on the road twice during the week. Your long ride is at the weekend, so go for quality in the week. 90 mins for one ride and some long intervals with the other - several efforts of 10-15 minutes with 5 mins recovery. You won't get much climbing done around Selby, but those railway bridges can be deceptive
You can use the club events for a good work out and a bit of fun when they start in May.
Hope the above helps - its not exactly radical is it?
Good luck.
R