Okay, so a further update on this. Things didn't go according to plan.
On the turbo, where I'm not changing gear, everything seemed to be find but once out on the road, it really wasn't. Despite the Shimano guides suggesting everything should work, it just didn't. On the large cog at the back, it kept rubbing, the front shifter kept throwing the chain off on the inside and it wouldn't run properly on the big ring either. I spent quite a while watching park tools YouTube channel, tweaking everything I could but nothing would work.
So, I took it to a great bike shop we have locally and had a chat with them. They had it for a couple of days to try it out and see what they could do. Upshot was that none of it really worked together properly. He said he looked everything up in the book and agreed it should have worked but it just didn't. The new chainset just wouldn't work with that shifter and the rear, despite being within spec, wouldn't work either. Being 10 speed, nothing new really works with it so we were into changing derailleurs to try and get that working. The mechanic was pretty sure that he could find a suitable solution.
Couple of weeks go past and we have a mountain bike derailleur that works correctly with the pull of the 11 speed shifters and it runs the back nicely, with the advantage that I could go up to a 36 tooth if needed. The front needed the outer chainset guard removing and thinner chain ring bolts to attach them without it to try and bring the derailleur further out on the big ring. That still didn't work so a second hand derailleur up front did make a big difference to the shifting but it still wasn't quite right. They also put a narrower bottom bracket on to bring the chainline in a bit closer.
They then changed out the chainset for a Kranx 50/34 compact rather than subcompact and it worked perfectly. Changed it back to the subcompact and it wouldn't so we're now on a compact chainset. Also put a barrel adjuster inline on the front shifter cable as there wasn't one on the bike itself so it can be fine tuned more easily.
Everything is running very sweetly now but I have a sub compact chainset, bottom bracket and a couple of derailleurs in a box. Mind you, I also have an old 90's trek mountain bike sitting not doing very much so I'm looking at turning it into a gravel/bikepacking bike as a winter project.
Gearing wise, I'm currently at 101-30 with the 13-30 rear cassette. With the Miche cassette I can change individual rings but there are limitations with what can be at the top and the bottom. So I'm thinking that if I went to the 14 instead of the 13 my max pedalling speed would be 25mph which is plenty, I won't be pedalling faster than that but at the other end, the only rings Miche make larger than a 30 are 32 and 34, which would drop my gear inches to either 28 or 26 instead of 30. 26 is where I was on the subcompact chainset with the 30. So I'm tempted to go with the 24 but is that too big a jump from the 30? The cassette would end up being 14-15-17-19-21-23-25-27-30-34
As an aside, the mechanics had found the bike a fun project to work on as they'd never seen a bike like it, I think it's the only one in the country. They also said that even when parked next to bikes costing several thousand pounds, it attracted a lot of attention from the various cyclists who came in to the shop, which made me smile.
