Hahaaaa!!Giggled when i saw this thread pop up!!
First of all may your endeavors bring you the pleasures you are looking for and may you have all the good luck in them!
Now to the real part..
I will start with what you started and that is the hood! I will first notice out that
i left my 600w MH on for less than a minute without the fan on and the inner cables-the coated ones got black,that said,first get a fan and then get the lamp running!! It is a sealed hood is it not?
As for fan,i have a 125mm VKO exhaust fan (183m³/h) that suck air from the hood/lamp and throws it out the back top outlet i have in my tent!
The other side of the hood is connected to ducting that leads to a window where cool air is sucked into to move through the lamp!
This exhaust fan is just hanging of the bars in the tent,attached to 2 pieces of ducting (from the hood to the fan and from the fan to the filter) and is sufficient in creating a 2,5" deep curve for my 4.5x4.5.
It is also sufficient in cooling the MH/HPS(600w) down to 23Celsious when the glass is in place,i remove it for this grow as the plants seem to like it!
You can use just an exhaust fan and you can do fine,it really all depends on what you want to do!An inline fan pulling air from a hood into a ducting is quite good!!Are you having your filter inside or outside,that is something you want to ask yourself!! It will help you place your ducting right and then you will know what kind of fan to use and where ot put it (outside,inside for the filter\exhaust or inline fan)
Not to bump
LuckyAcres but it really depends on your strain about the humidity,i have 49% lights on 57% lights off and im doing fine,growing indica based hybrid bred specifically for humid areas tho

Also autos can withstand humidity and mold unlike photos!!Ruderalis is a strong damn gene!
I have not recommendations on soil esp US based products but most people here know them off by heart!
About the scrog,i wouldn't right away, i would say go with lst,defoliation and OR manifolding at first!It is in my belief that scrog is kinda harder to do right and harder to right your wrongs in the net...Thats just me and hey,im doing extreme things i shouldn't on my first grow so who am i to stop u....
What ever you do,keep it green matie!