About the waitress job at the bar:
Is there any advantage to getting the editcs for new drinks, do I get new scenes/poses for having them?
Having more drinks just seems like a pain in the ass to remember who ordered what when I can just walk around with 3 beers all the time.
Also, is there any way to know how drunk Karryn is before she triggers the scene with the mug between her breasts?
TL;DR: no new scenes, just everyone drunk faster and a lot more money; the more drunk she gets, the more seconds she needs for actions (a small amount of alc is enough, but hornyness also increases the time; cock desire is the key to trigger the scene).
But the edicts for more drinks are worth it in two ways.
First, they directly increase the bar base income which scales with the bar reputation. As an example, the first edict raises the base bar income by 100g from 150g to 250g and generates an expense of 75g. While it may seem as a profit of only 25g, the modifiers are what makes the difference (especially with the second and third edict). If you have a bar rep of 20 you get 50% more profit from the bar. That means a flat profit of 75g each day. That's okay, but not great for an edict that costs 500g.
Secondly, all new drinks are more expensive than the old ones and they are stronger. A list directly from the code:
Advantages: more passive income (from edicts, scales with bar rep), a lot more money in the form of tips, they get drunk faster (less maintenance, because asleep or leaving the bar drunk)
(Dis)advantages: no braindead ale transport anymore, she get's drunk faster if persuaded to drink
Personally, I always get the first one fast and get each subsequent one at some point, if nothing else has more priority.