Get a few hammocks :) Rats love hammocks. Our girls cage has 6 in at the moment, we have bags of the things.
We find carrots also produce extremely smelly poos, just as another warning RE carrots 
Porphyrin from the eyes can be a bit scary, moreso than from the nose. Ashi is the only one of mine to have "flooded" porphyrin from his eyes, the others have had it but only slightly, but after giving Ashi a bath when we first got him his eyes flooded with it as if it were red tears. Bloody freaky.
Make sure that the bathroom is rat-proofed before you take them into the bath though, they can get through very small gaps. One of our big boys went through this tiny gap between the wall underneath a built-in under-counter fridge the evening we got him. He hadn't even reached his cage yet. There is a gap through to the bathroom and he was under the completely sealed up bath for the night, the little sod.
Rats don't seem to use wheels often, we have a couple but our boys don't touch it at all, nor does our little loner, only the girls use one and even then it is more likely to get used as a toilet.
This girl does amazing hammocks:
www.rataccessories.co.uk/
The clammocks are fantastic.
Ours are all polysomatic, but definitely more active in the evenings and early mornings. Right now 6 out of seven of mine are dozing, if I opened a cage they'd happily jump up to play or see what I was doing though. It's usually early afternoon where it's "wake at your peril" 
One has just been shoved off of a hammock by her sister, so I have two now running around 
I love rats, they're so funny to watch as well as to be with. They're so full of personality as well. All of mine have been so different. I want a baby one again now. I'm getting a new girl in August/September and cannot wait :)