damn alot of ?'s
you should look into some DIY(Do it yourself) hydro bubbler's... in other words the rubbermaid SOG systems.
pic attached at the bottom. You will want a bigger one than that though.
250 is got for 6plants in a SOG(Sea of Green) not 6 big plants a 400w can barely handle that.
check out this link about the seeds and the sites;
https://www.rollitup.org/seed-strain-reviews/108893-how-mane-how-order-seeds.html
A good indica is great for the DIY Rubbermaid, you don't want a sativa in that kind of system.
Chemicals? Nutrients well I'd say Ionic or General Hydroponics Flora series are great for newbs.
I really don't fell about thinking about everything you need, but I'll throw some of the things you'll need.
Air Pump
Airstone
Timer
Surge Protector
Space to grow lol
Rubbbermaid
net pots
hydrotron
Nutrients
Ph meter or test drops
TDS meter(not required)
Mane