Aww, your hides are adorable! I'll need to find a tutorial on how to make those. I'm sure my boys would go crazy for them.
As for baby wipes, use the unscented variety. I don't know if you have Target in the UK, but I use Target's brand for unscented baby wipes. I use them to clean down plastic hides, wipe any urine or anything that's on the bars, their levels, etc. Anything unscented is the best for rats, including no scented candles, no aerosols, unscented bedding, etc. Anything scented can lead to issues with breathing.
I think it's definitely worth covering the bars with some fleece. Personally, I think it's just painful to watch them walk on bars.
As for litterboxes, it's up to the rats. They tend to poo and pee in specific corners of the cage, and those corners can differ from level to level. Once you find those specific corners (whether it be on just one level or every level) go ahead and place down some litterboxes. If there isn't enough room for a litterbox, go ahead and manually move the poo to the litterboxes to teach them to potty in litterboxes and not there. My boys decided they wanted more littrboxes by pooing in another corner, so I gave them another litterbox.