He's gorgeous - agree about that awful cage - too small and the wire shelf. The other one is a bit on the small size floorspace wise but not bad. The height is an issue - too high for a hamster. But the middle section is lower. So if you could block off the other two "towers" at that height it should be ok - depending on the internal height of the middle section. Eg put a full shelf across the base of each tower to just block off those areas.
But to be honest you'd be better with something like the Savic Hamster Plaza which has more floor area and less height. It's still slightly on the tall side for a hamster but fine with enough depth of substrate in and set up so they can't fall on anything hard or sharp if they happen to climb to the top and monkey bar across the roof.
Unlike rats, hamsters aren't great climbers. They will climb (to see if they can get out of the top) but then can't get down again and don't see well, so they tend to just let go and drop - and get injured! They are more ground dwellers who like to move substrate around, bury things and burrow down.
Having said that. The rat cage you have is not too bad if set up carefully. I just think the floor area is a bit below the minimum needed for a hamster (usually at least 50cm deep) - but not too bad. If set up carefully.
He'd need a 28cm wheel, a solid shelf (to sit under and sit on and somewhere else to go) and a good sized house/nesting box at floor level - ideally dark inside. A shoebox house is good. Plus a few tunnels/hidey places at floor level and at least 4 to 6" deep of substrate, and plenty of nesting material (torn up strips of plain white toilet paper in a pile in the cage - they forage for it).
Safety wise, no chains, open rung ladders or fabric. Cardboard, wood and ceramic are your friends
And some plastic items.