I think they'll be just fine, they'll get used to the noise quickly
I also have fleece but an area of Fitch bedding and hay for them. All four piggies do the majority of their wee's in the Fitch bedding, skirting round their hay. They do wee in other places too, but not much. They definitely prefer 'litter' for their wee.
Oh and as for space, again I think they'll settle in very quickly without having to put them in their cage at night. They'll be just fine
It's a lovely space for them
Are you going to make it so that the front panels can be opened for cleaning?