I think you can host on warm showers for free without paying the membership.
I was happy with the bikes, only issue we had was my gears had 2 major failures throughout the trip, one just as we were leaving Edinburgh, towards Dunbar and another next to a canal in Belgium. First one was where my chain got caught on my front chain rings as I was changing gear, this pulled the tensioner all the way forward and broke a bit off of it, it still worked but was never quite the same.
The second time the bearings in my jockey wheels fell apart and locked it up solid, had to take them apart and use tape to fill the gap until we could get to a bike shop. First picture is how it looked when I took the jockey wheel off the bike. Second is what was left of the tape after 15 miles of cycling with it.
As for the bags I think I will re make them at some point to include some of the things I wish they had (bigger opening, slightly thinner etc). I liked the roll top and how they were attached to the frame, also having a small hole for a charging cable was really useful.
As for future rides, a tour around Scotland is definitely going to happen at some point. I would also like to do northen Europe again, maybe following more bike routes and at a slower pace so we cam see more things. One reason we tried to stay off th main routes is to increase our chances of warm showers hosts however that didn't work as we got none anyway.
My gears were making some weird noises for about 10 miles before. They were cheap metal ones, some better plastic ones with bushings rather than bearings would be more reliable. I ended up replacing the jockey wheels on the hardrock aswell as they were so worn the chan was rubbing on the cage. No sure I would bother carrying some though. They are basically standard across all rear mechs for the last 30 years so every bike shop will have the right ones. You can also bodge them easily if they break.
As for Scotland, the weather can sometimes be brilliant, it can also be terrible and is very hard to predict. You just have to plan in the extra time if it's too bad to ride that day and always have a backup/escape route if things go south. The miggies can be a problem although some good quality bug spray, combined with avoiding dusk and dawn outside, some long sleeved clothes and a net for if it's really bad, it won't be an issue