Single Auto Plant Setup

I've decided to try my hand at growing... in a 23 foot rv. We use the bath house at the campground we're staying at so that leaves the stand up shower open for a plant. I've done tons of research and I'm on a budget so I'm not too interested in buying high end supplies for a single plant so I'm trying to make do with whatever is cheap. Here's what I've got:

Auto amnesia seed
3 gallon geopot
Half and half eco scraps organic/natural and miracle grow organic
138 watt led grow light
Diy carbon filter vented outside with a 79 cfm pc fan

I was thinking the soil will give plenty of nutes for most of the time and maybe supplement a tiny bit when flowering starts. How far should I keep the light from the plant as it grows? If you have any suggestions I'd love to hear any

Add 25% perlite and make double, triple sure your mg soil isn't "moisture control". It doesn't drain well, it holds moisture too long. Your cannabis roots will need more oxygen than it will provide. There are multiple bloom amendments if your trying to grow organic.

Will add perlite, I knew I was forgetting something in there. Nope, doesn't say moisture control anywhere on the bag. I'd love to grow organic, but from my skimming tons of articles it seems like a lot of different ingredients to make sure to hit all of the needed nutrients. Do you think the soil would provide all the nutrients needed for a 10-12 week grow? I just hope that 138 watt is enough.

When you see the first pistils add a bloom amendment like Dr. Earth bloom, Jobes, or an Epsoma bloom or flower. All three of those can be found at home depot, lowe's, wal-mart.

138W isn't much light, you want to consider an additional light.

Upgraded to a 300w since the 138w I received today had a dead led. I got a good reading on the ph of my tap water. I've read that you should let it sit for a day to evaporate something or other. Does that actually make any difference?