It's an amazing set up and clever use of a cage top. My concern looking at it, aside from possible ventilation issues as mentioned above, is the fall risks. It is quite a height to fall from the cage bars to the bottom of the detolf and then landing on all the hard wood items underneath, some even pointed. Which could cause injury.
I would suggest that any toys are moved from the area underneath the cage top, elsewhere, and deeper substrate is put in that area, so if your hammy did drop from a height it would be a soft landing.
My own experience is that hamsters only really climb to try and find a way out! When they have plenty of enrichment at ground level and a big enough cage, they often don't bother to climb - unless it is to access something they can't reach or to try to escape.
Now your hammy has so much space, the need to climb isn't really important - and they can have different levels in the cage for variety of texture and height, plus large cork logs are good for climbing over and running through.
I would be a bit careful about hanging toys in the cage part as well - I can't see them well but a hamster could get a leg caught and end up hanging by a broken leg if there are any open rung ladders or chains/rings attaching toys etc.
Just highlighting a safety aspect to look at but the set up is lovely.
I personally think it will need more ventilation and an easy way to achieve that would be to install small round vents into the wood end panels - people do this with vivariums to improve ventilation for hamsters. This kind of thing (top of the page)
https://www.amazon.co.uk/s?k=air+ven...f=nb_sb_noss_2