Ah he sounds a lucky hammy to have found you. Flying saucer sizing is funny -there is nothing between 6.5"/7" and 11/12" I believe! But the 6.5/7" is perfect for a robo and ours runs fine on his - he jumps off sometimes for fun (and sits in the centre and spins round sometimes too!). At first they do fly off it sometimes but they soon get used to it.
In a standard wheel, the 8" wodent wheel is good for a robo - in Germany they call it the robowheel. Exotic nutrition in the US sell wodent wheels. I think the small round holes on it are good for a robo as they can't fall out or jump out while it's spinning.
As well as Kaytee Clean n Cozy there is also Boxo in the US (sold by Walmart I believe) which is sold in bulk so suppsosed to work out cheap - soft recycled pieces of cardboard. And you can also mix two or more substrates, so mixing Boxo and Kaytee Clean and Cozy would make the KTCC last longer/go furhter and work out a bit cheaper - but using either on their own is fine as well.
They also need nesting material - plain white toilet paper is best (not scented) - a few sheets torn into strips and then a pile of the toilet paper strips in a heap somewhere in the cage - but not actually inside the house. They like to forage for it, and pouch it or drag it back to where they want to build the nest (or line an existing nest).
If using a water bowl, I think caution is needed with a robo, so they don't fall in and drown, or get soaked and get a chill or tip it over and have no water. Our robo uses a bottle absolutely fine and I think that's a bit safer with a little tiny hamster. The water bottle I found good in a tank was the Ferplast Sippy bottle which comes with a holder with a suction cup, easily lets water out and our robo could easily use it.
But many people just use industrial strength velcro to attach a bottle to the side of a tank and it works very well. There isn't really a chewing risk if the pieces of velcro are small enough not to be very visible and well behind the bottle itself. Then you can use any bottle. It is something that needs keeping an eye on with robos (being able to reach it) as if it's over substrate, and they tunnel under, the substrate can get lower in the bottle area.
I had lots of nice little houses and hides when first setting up our robo's tank and he ignored all of them and dug a tunnel/hide under a shelf and made a big mountain there to disappear down under
He didn't use a house until I got him a large labyrinth house, which is dark inside - and even now he has two nests - one in the house and an "emergency one" under his wheel which he uses if I do anything inside the house (spot clean) and eventually moves back to the house again. They are funny little things and they do like digging tunnels!
They are scared by a lot of open space so lots of floor toys like tunnels or a small level/shelf in one corner, go down well, so they can move around and always be underneath something. Although when feeling braver they move around without being under something, but like to have something nearby to dive under.
This is the Ferplast Sippy bottle. It comes with two attachments - one for a cage and one for a tank. The suction cup worked very well - occasionally one side would come unattached, but easily stuck back on again - and never did both suction cups come unattached at the same time so it never fell down - just needs checking now and then. Wetting the suction cup slightly on the tank side helps it stick well.
https://www.amazon.com/Ferplast-Hams...y+water+bottle