If he is going to be 5 months, I would recommend getting a bigger cage because in a couple months he will definitely need it anyways. You can create a simple drainage system by removing the bottom (leaving only the screen) of the enclosure and putting a removable water tray underneath, which LLL Reptile sells on their website. As far as misting, if you can mist four or five times a day by hand for long periods of time that would work great, but otherwise I would suggest getting an automatic mister such as a MistKing. As for lighting, it seems you do not have a problem with temperature differential, but if that comes to be one, I would go lower wattage and focus the basking light in one little corner. I always believe adding more plants is always a good thing, that is mentioned earlier if you can keep them healthy. Ficus are great options as the fill out to be pretty big plants along with schefflera. I'm not quite sure how to answer your misting question, Usually I have never had a problem with mist/water escaping the cage. You might just want to focus the nozzle more straight so water does not spray all over the place. And yes, you should probably remove everything on the bottom of the enclosure when cleaning and wipe out any feces/sheds/anything else. You should probably thoroughly clean your enclosure once every month or two.