Do you have any suggestion for how to phrase a question about a mechanic so that is abundantly clear the information sought is about that mechanic, not more or less clever ways to avoid using the mechanic in question?
Well, your original question was pretty much answered: No, there's no way to achieve the situation you outlined using only the manager interface.
Furthermore, it is not actually possible to specify a particular type of plant for brewing. That's done through the (d)etail option, which isn't available for brewing or any of the other jobs that use plants. It's important not to get it mixed up with (c)onditions, which are only the conditions that must be met to trigger the order starting. You can have a job trigger
based on the number of pig tails, but that job won't necessarily
use any of those pig tails as reagents.
For your second question: Conditions that are checked monthly only consider whether or not the conditions are met at the precise second of the check, and if so, trigger the order to "active". Once an order becomes active, it will keep generating jobs until it's filled, regardless of item stocks or time passed. Condition checks only happen when the order is inactive, because they are
start conditions, and the game logic dictates there's no reason to check whether an active job needs to be started again until it has finished.
So if you have 11 plants at the beginning of the month, your "brew 10 plants when plants > 10" will switch over to "active". If 9 of those plants are then eaten by dwarves, the job will brew 2 plants and then continue spamming brew jobs until it can finish the other 8. Even if another month passes, it won't bother checking the conditions again until it has successfully brewed the 10 drinks you asked for.
At least, that's been my experience so far. It's actually a fairly desirable behaviour if you really need a certain amount of something because it powers through supply interruptions, but it's pretty clunky for background automation.