Good to your doctors or maybe local chemist and try to get some empty saline drip bags. There are made of thick plastic. That’s what I use with my springer for walks when they injured their feet
Also try the vets
I think you need to join, no problem in that. By the sounds of it your kennel will be more than big enough. Mine will be 1.5m wide by 3m long with cabins inside that, housing 2 spaniels. Personally I would go for the rendered finish.