OK if the advice of someone who's lazy and not afraid to admit it, is any use: doing 50 miles in a day (or even more) is one thing but if you're touring you're riding everyday. I think the best 'training' would be simply to go somewhere for a weekend - say 50 miles there and then, next day, ride 50 miles back. If that works out OK (as it should) then you can extend the distance, or turn it into a long weekend - ie 3 days at 50 miles each.
Yes OK £50 for a saddle is a lot if you're on a limited income, but on a longish ride having a saddle you get on with is going to make a huge difference (or at least a saddle you don't get on with could make the whole thing a real penance). Buying a cheap saddle could be a false economy. There is a 'saddle library' which means you can borrow a saddle to try it out. I've never used it, so I know nothing about it, but you might want to check out this link:
https://www.cyclechat.net/
Yes OK £50 for a saddle is a lot if you're on a limited income, but on a longish ride having a saddle you get on with is going to make a huge difference (or at least a saddle you don't get on with could make the whole thing a real penance). Buying a cheap saddle could be a false economy. There is a 'saddle library' which means you can borrow a saddle to try it out. I've never used it, so I know nothing about it, but you might want to check out this link:
https://www.cyclechat.net/