Looks like a good start. If you do like me I'm always changing things to try to improve. Have you considered maybe a duel 150w instead. Should spread the light better over the canopy. I'm not sure what you mean with the 3" rings for an intake? Maybe replace the bath fan with 2 computer fans. It would be much quieter and a better longer lasting fan. Looking good though and I'm looking forward to seeing pics of it being built. And with the 120mm computer fans you can bolt 2 toilet flanges to them and make an inline fan cheap and very easy. Some flanges don't even need any drilling, the holes line up and you just need to bolt them together.