I doubt a "less potent form of drugs" will happen exactly as you imagine. Drug potency has skyrocketed because logistically it's easier to smuggle smaller quantities of a high potency substance. I personally think we would see a resurgence of drugs and doses of what people were previously doing before importing them got so difficult. What would be interesting though would seeing if any new analogs could be discovered with shorter term effects especially in the world of stimulants.

I disagree as what looks more suspicious, a computer with tor on it or a computer that has nothing on it because tor is on your flash drive?

Avoiding escrow isn't really possible unless you somehow live in a perfect world without bad actors. I recommend doing some digging into how different defunct darknet markets have utilized escrows and monero as even if your market does everything legally there's still valuable leasons to learn. If you want recommendations you should look into White house market (mods it's defunct) as their system handled escrow in a way where everything happened at the transaction level meaning the only coins that could be stolen were the exact transaction ammount.

Effort? What effort? Putting a bunch of sugar into juice and letting it sit for a couple of months takes almost no effort.

Want something stronger? Put your newly created Cider in the freezer for a few hours then remove the ice. Congratulations you just freeze distilled your Cider in jack (nearly 30% abv)

Seeing how easy homebrewing and how well documented it is online...

Lots of people buy random ass gas station "supplements" as some are research chemicals being sold under other names. Unfortunately the real fun stuff no longer pop up after the DEA cracked down on it. Here's some examples of different RCs that were sold in gas stations.

2C-B a serotonergic psychedelic was sold as an aphrodisiac under the brand name erox and nexus

MDPV and 4-MMC two empathogens similar to MDMA where sold as "bath salts" under several brand names including ivory wave, purple wave, and white knight

Famously a whole bunch of synthetic cannabinoid were sold under the brand name K2 and Spice

DMAA a stimulate was sold under the brand iced diamonds and many other brands

Silk road is long gone but there are a plethora of other similar markets. Just like any other service in demand when one gets shutdown three more pop up in it's place.

A federated marketplace could be interesting but there are some fundamental issues that would need to be addressed.

If the vendor and vendee are on different instances how will payment be securely transmitted? What if there is a dispute, which instance Admin would have final say? Will the instance operator get a cut, if so how does that work? What's stopping my competition from opening an instance to check my stock level? What if I want to buy multiple items that are on different instances, do I have to check out on each instance?

If you can iron out the kinks this idea could make a lot of sense as a DNM as there wouldn't be a centralized server to shut down and being FOSS would allow for auditing of the marketplace which just isn't possible currently.