Cycling-Related Strength & Conditioning

Right. You chaps are well up on your fitness know how so, in a nutshell, I'm feeling like I've really losing shape over the last year through being really unsettled and moving round a lot so I'm wanting to set myself a goal for next year and do a few sportives leading up to either l'etape or marmotte in summer. Am I being totally unrealistic to take something like that on? a guy I know that's done it says you need to train 2 years in advance to have good core fitness and also get a lot of experience riding in packs. I get out on my bike for long rides when I can (50-75 miles normally) but it's mostly short commutes during the week,

A lot of sites tell you general info about how many miles you should be doing per week in the lead up to something like the etape but could/should I be complimenting this in the gym/doing spin classes, or at my level is it just a case of htfu and get a better alarm clock and some thermals for long winter miles?

I did the etape last year from doing very minimal road cycling beforehand. I followed a training plan from the book Successful Sportives and started training in November. It was very hard but managed it a few hours within the cut off.

Pre Xmas training was all on a track bike doing laps of Richmond Park, after I started going on club chaingangs, doing turbo work and longer rides. If your aiming at this I would do very minimal if any gym work, you really need to get the miles in so time spent lifting weights takes it away from your cycling.