I have done a few more tests on the temps and the temp started to rise to the high 20's with the 120mm fan . I believe this is because some of the 120mm fan had to be blanked off due to its size. So I swapped it for an 80mm one and it fits perfectly and I can confirm it keeps the temps in the mid 20's so I'm well happy.

As for the smell, well I lit a blunt in it and left it in there smouldering for a few mins next to the filter and got absolutly no smells coming out so I'm going to assume that the filter will be good for a few microplants.

As for vedging with a hps, well I know a clf grow light would be better but that would defete the object of the project so it will very much be a 'try it and see' approach to it. I think the worst that will happen is they will stretch a little bit.
It's currently not doing anything as I am having a few issues getting my seeds (for my seed run) to germinate.
But I will keep you updated as soon as its up and running.
I think this should be an awesome little box.