The coco is brilliant, though I wouldn't have small girls or young ones in it as the gaps in the corners can get quite big. The whole bloody metal thing falls apart when you remove it to clean inside though and takes a bit of practice to put back together. But we used ours for a good year or so and I was able to clean it out alone until I was 6/7 months pregnant so it wasn't that bad, just a pain, definitely one of the better ones we had before finally investing in a savic royal suite. Currently have half of that up with 3 girls in it.
We had the short little friends blenheim as a spare cage and also a a cage for a loner with epilepsy, the massive door on top was fantastic. Aviaries make great eat cages too though you need a lot of hammocks to break falls as falling from the top could seriously injure a rat. We had a young girl who managed to miss all of the hammocks on the way down and break her leg, six weeks to recover from that one fully, which is a long time for a rat, they usually recover very quickly from injuries, though she did go back in the cage a sprain it within a day hence the six weeks. I would recommend a small cage or a single layer height cage as a hospital cage, you can get them cheaply online and they are handy if you need to transport them or keep them from climbing too much if they injure themselves. Handy for when you want to clean them out without fishing them or off the bin every few minutes too!
Some can scent mark but I've only ever had one who did it excessively and she had bladder issues (among other things!).
They can smell but substrate makes that less, I find fleece makes them much smellier. You can buy bales of cardboard substrate which we find brilliant, trata should ideally not be on wood shavings, it's not a dangerous for them in the UK compared to us (where you hear all the horror stories from) but it's still not great for them, though we had a pair on it as one seemed to be allergic to every bloody type of substrate we tried 
he lived the longest out of all of our rats too funnily enough! After about a 18 months or so we found that paper based cat litter worked for him but that got expensive so we switched to the cardboard this year long after he was gone.
Ideally you want them out as much as you can, at least an hour a day tbh, cages are not big enough for them to spend all day every day so free ranging time is important along with time with you.
Ratrations is awesome, we get our bedding and food from there, I buy loads of food on bulk and make it up every 6 months or so, though I think I'll go for one of their premixed food mixes this time as we're running out again. Fresh food is important too, ours get some of our dinner quite often and fresh fruit or veg too. Cucumber is great for any time you need to take them out somewhere as it's got water in it, so handy for keeping them hydrated if a water source is difficult for short periods (like in the car or vets, not anything more than a few hours at most!)
Always get rats from a good breeder too. The nfrs list is a good place to start but you'll find good breeders who are not on it locally too. A lot of ratteries have fb pages these days where they'll share photos of litters and parents and people can comment and review them, there is auk Rattery and breeder reviews group on fb too which is handy, especially for avoiding back yard breeders.
Is also advise having around a £100-200 on hand ready for an emergency vet trip. Not common but it can happen, I think £150ish was about the most expensive trip we had! And research vets beforehand, you ideally want a rodent specialist or exotics vet as a lot of standard pet vets have no clue with rats. Rats get respiratory issues often, it's something you'll come to get to know as you have rats and you'll work out when you may need treatment, but they're hardy little things usually. The only other major health issue is that girls are prone to tumours, so sometimes they have to be removed. I've found my ones from breeders have suffered less than rescues we've had but that may be coincidence. We've seen a lot of the vets as we've had three special needs rats and a few accident prone ones along with a couple of emergencies over the years, you're not likely to see them often though, the last few months of a rats life can be when you do though.