There won't be any new custom drugs added for a little while, due to the amount of work required to add them. There will likely be a bunch added at once the next time we do. I'd like to add more custom drugs that are crafted with drugs that aren't sold much at the moment, and with sugar being a very popular drug, it's unlikely that another sugar recipe will be added.
The villager suggestion would be a lot of work to implement, and I just don't see it ever being added.
Booster tipping is something I've wanted for a while, but it's not possible with our current plugin. We're getting the plugin updated (also to work with cross-server/world muling), and this will be a feature when that happens.
We removed the ability to use drugs for a few reasons. The way that they were used (shift + right clicking with the drug in your hand) caused a lot of people to accidentally use drugs while trying to plant them, and this could result in them overdosing and losing their items. The effects of drugs also weren't very interesting or unique, so in my opinion removing the ability to use them isn't an extreme loss.
I'd be interested in bringing back the ability to use drugs, as it adds a lot to the roleplay side of the server, but it's not priority at the moment. If anyone has any suggestions for a new way to use the drugs, or the effects of a certain drug, feel free to make a suggestion.