in OP's post it's not drop shipping if you physically ship it yourself. Drop shipping is if someone is handling the shipping for you, the producer itself or one of its distributors.
I don't think that the DTV was meant for that. You're in the same category as digital nomads and remote workers. Do you see the difference ?
I'm very skeptical that producing physical goods to market online and ship through customs is allowed. But hey , I might be wrong and could rent a Warehouse, fill it up with stuff thousands of handmade candles, paintings and soaps and sell it outside of Thailand under the guise of freelancing on DTV instead of saying that I started a business 🤷🏻♂️
It would perfectly make sense to have to show funds again for an extension. The opposite would be surprising as it would make the requirement when applying kinda moot.
As far as showing proof of funds for a report after a new entry (If I understand correctly the wording of OP) that's sketchy and maybe something has been misunderstood by someone or lost in translation.
Lawfully, If you stay even 1 night at a family place , your family should do the TM30 yes. If you don't need immigration service, then up to you I guess.
But the rule is that any hotel, or head of household is required to do a TM30 for any foreigner residing at their place within 24h