I'd the opposite.
RUN broad - since you probably don't have any pixel data.
Run broad, target males 25-54. (I assume that's the gender & age group of your core buyers - no?) and don't include any interest targeting at all.
Optimize for conversions - Make it CLEAR in the image what you are promoting. Without using text (this is called meme).
So you want to use THIS sort of images:
NOT this kind :
The 2nd kind isn't clear enough .... people will be confused.
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In the ad copy do NOT mention weed/marijuana. You might want to use coded language that only other pot-head would know i.e 4-20 and that sort of stuff. You don't want the reviewers to catch wind of what you're promoting or you will be banned.
Here's their policy: facebook.com/policies/ads/prohibited_content/drugs
I would HIGHLY recommend you focus on building an e-mail list instead of sending visitors to your store.
Offer them a useful guide on how to grow 420 trees.
And include in the e-mail a branded ebook with useful tips and some of your best equipment.
This is a specialized niche - I'd charge him $2k/month for this service - but since you're new - charge whatever you're comfortable with right now.
But down the road, when you know you're bringing him results via e-mail marketing and your efforts - charge $2k/month.