I’m opposite, ‘all Leg’ I’ve been sizing bike frames down for a few years now, arguably just the right size considering most manufacturers size charts don’t seem to be that accurate. Longer torso is probably less of an issue considering you can adjust height via seat post but you can only reduce or extend reach so much via stems. Most of the answers to your questions are, it depends. What you’re able to tolerate, bike you’re riding and what you’re using it for. Position between an hour crit and 5hr endurance are understandably different

Check out geometrygeeks Fag packet comparison, closest is 49cm based on frame only. Depending on current set up, flexibility and what you want to use the bike for, you may need longer stem and a number of steerer spacers. They’re very different bikes

I’d revisit the bike fit, explain the issues and go from there. Feels to me like the start point is to get back to the position set up and then look at saddles. Ultimately it sounds like you’re not sitting on your ‘sit bones’

Given these events aren’t races, the training required is fairly simple assuming you have a reasonable number of weeks to prepare. Muscular endurance is the focus, essentially the ability to repeat the same thing over and over. You should also consider fuelling too. On work days aim for an hour, zone 2. First day off plan a longer ride, 2-3 hrs for a couple of weeks, then build to 3-4hrs before 2 weeks out from even aim for around 4.5-5hrs. Use second day off for an hour very easy, 3rd day off, shorter ride at higher intensity. Use 4th day for rest. Most of all you need to add volume as you go over a number of weeks to make sure you recover in order to absorb the training effect.

I have this, almost the same discs narrowing. The solutions will vary depending on how your symptoms materialise ie isolated to left or right side, buttocks, thighs or lower leg but a few general things first. You will find a series of simple stretches on youtube which might help particularly during ‘flare ups’ For the bike, symmetry, the best you can possibly get was key for me. Even stance, a supportive saddle (I went narrower to avoid sitting off to one side). I also found that a too upright position put more weight on lower back therefore a lower front enabled me to rotate forward to alleviate pressure. Lastly, my max being off the bike is 3 days. Its almost as though day 4 getting on ‘the nerves’ becomes used to not being in cycling position so 10-15mins light pedalling antagonises. During my worst period, I started to see a chiropractor 3 times a week for a month, this then reduced to twice, once and now I do one session every 10-14 days. I find regularly decompressing the spine is good for me overall helping with sleep, cycling and general well being. Its a toughy, but you will hopefully find a way through it. In 2021 I thought I’d have to stop cycling and sell my bikes. In 2023 I started racing