It's a great cage! Apart from the external tubes. This is a common problem and best advice is remove the tubes and block them off then get the cage set up in a way that allows them to have normal behaviours
. He will definitely need a wheel - they go stir crazy without one and need the exercise. But the one it came with is too small to run with a straight back - a good basic option is the 28cm Trixie wheel which costs about £9 (linked below).
I don't think it would take much to make your set up so your ham feels happy and cosy in there. The main things to think about are
1) Nesting and hoarding
2) House
3 Wheel
4 Access
So you could do to add a lot more substrate - at least 4"deep - this helps them feel safe at floor level and able to move substrate around where they want it and bury their hoards in it.
They ideally need a house on top of the substrate that is open underneath and dark inside. That way they can bury their hoards under their nest and burrow down a bit to keep warm.
With those basics they feel safe and secure. It's an instinct to block up their house entrance to stop light coming in so if they nest in tunnels they will keep blocking the tubes up!
Access helps them feel at home as well - as in being able to reach things and have them have a purpose or be usable without them feeling insecure. I think the long bendy bridge above the shelf is ok but he may feel a bit like he'll fall from it - on the other hand it gives something to sit under (so overhead cover) - maybe lower it a bit.
I would remove the little pod house on the shelf or he may decide to nest in it - they like them because they're round but they're not big enough to hold a nest and hoard and so, like the tubes, would end up needing cleaning out a lot.
Id put the wheel at the other end of the cage to the shelf and remove the hanging ladder - chains are a bit dangerous (they can end up hanging by a broken leg). Theyre not natural climbers and are more ground dwellers. They don't see well so fall off things easily and can hurt themselves - which is ok in that cage as long as there is plenty of soft substrate to land on!
So you could move the wood house a bit to make room for the wheel and maybe add a couple more floor toys - eg a kitchen roll inner slit down the side (so it expands or they can get stuck). You could use a length of the external plastic tube as a floor toy - if it's big enough - some hamsters can get stuck in those if they have full pouches.
Just off to look at your pictures again