Sounds interesting! Do share any good projects you make! Hamsters aren't that interested in climbing really - unless it's to look for food or an escape route! They do climb but they're not good at getting down again so tend to just drop if they climb too far. I'm sure low climbing toys are fine though.
Some childrens toys can be interesting in a playpen too
We had the Octopod which was perfect for a hamster - he ran up the tunnel and into the control room and into all the little pods! He has also been in a jeep and on top of an x wing fighter lol
You just need to check the toys for safety in case there's anything they can get stuck in or hurt themselves on.