Hi welcome! He is on the small side and should not have been sold but with good care he should do well. As others have said adding live plants is a very good idea.
The 10.0 tube is fine. You are correct in the fact that the mesh will filter some uv.
A 6% T5HO gives out more uv than the 10.0 bulb so if the 10.0 is deemed too strong the 6% T5 HO bulb will be miles too strong even though both are fine. A 12% T5 HO bulb would not be too strong either aslong as the cage is decorated correctly. There is no longer really such things as one bulb for desert animals it is about the cageing, decoration and species. I personally use a 12% T5 HO bulb on all my panthers and they do fine. No bulb available is too strong when a cage is setup correctly.
In other words the uv bulb you have is fine!
I personally would add a dome over the heating as it will direct more heat downwards where needed. As the bulb is on a thermostat you do not have to worry about the wattage but a 40 watt bulb would probably give the heat needed.
I take it you are in the UK? I am a fellow uk keeper. if you need any help and need to know anything uk specific pm me and I will be happy to help.