They would be liable for a fine if they don’t provide you with a TM30. By law, they need to register you at their property within 24 hours of your arrival. They can do this online.
Just book into another hotel for 1 night and ask for your TM30 right away. No hotel receipts will not be enough. Sounds like they didn’t register you, therefore, both you and them will be liable for a fine.
with a normal business, yes you would need to employ 4 Thai workers. It’s only with the new LT visa that the 4 Thai workers stipulation is not compulsory. I have a friend who owns a bar and within that bar, he has a dispensary. No one has any issue with him selling cannabis products. It’s based in Chiang Mai, where locals and farangs live in harmony. If you were to open something in an area where Thai mafia were previously selling cannabis, for example (most places in the south), Ao Nang, Samui, you may face some issues from the locals.
there are many jobs that foreigners cannot do and farming is one of them. Growing cannabis would fall under that. Opening a coffee shop, doable. But who knows what Thais will do with cannabis laws… They might totally change next year.