LED Virgin

Hey my dudes I don't know much and so here I am asking a few questions.
I'm thinking of purchasing a 5x9 grow tent so first things first I guess that space will technically be reduced because I will have to leave space between the plants and the lights and also the lights them selves away from the roof of the tent, how much room do I need to leave between the lights and the roof?
How do i determine how far I need to have the lights away from the plants?
How do I determine how much lighting I need for any given space, how do I calculate this accurately?
I keep hearing 30W - 50W per square ft.
I want accuracy I keep coming across terms such as PPFD and PAR and I would like a better understanding of those.
I'm thinking of making the lights dim for veg as well so I would like to know how I can make that happen.
How do I determine the right heat sinks? I want to go with passive.
I have been watching a couple vids from Growmau5 really informative guy but I also like to do some reading my self and get opinions from the entire community as well.
I'll leave it at the for now guys, any info would be great or even just pointing me the right way would be super helpful.
Thanks man.

Look at ledgardner.com. read his blogs for the strip builds, watch his videos on how the meanwell drivers. Start studying the data sheets on whatever strips or cobs and compare them to the meanwell driver spreadsheet that led gardner created. He also has a tool to calculate drivers for strip builds.

The height depends on how hard you power the lights. Weather qbs, strips, or cobs the softer you run each one, the closer you can get to the canopy.

There is a few 5x5 builds on there already.