I work at a licensed store as well, much the same story. There is a lot to memorize and your first week or so might be a little rough, but just stick with it and it will all click at some point.
Customers are normally really understanding too so don't worry about dealing with Karen's and such. It's normally a rarity

also is dyed hair allowed

I'm a closer for one and I will say, most days are spent being alone and having time to clean which usually take me an hour to an hour and a half. Afterwards I spend most of my time going through the booklet we have in the kiosk for all the drinks (helpful as I too am, unfamilar with some drinks and like to read the recipes to familiarize myself) There are occasions where a surge of customers come through but I believe it's due to my corporate starbucks being short staffed so they close earlier (then their regulars come to me). I've seen crazy things as a closer so I hope your store is in a safe location (had a store customer do meth in the bathroom, that sort of stuff) and it's not so bad either. I actually love it and it's funny to hear customers tell me they feel sorry for me because I'm alone all the time, I enjoy it, no stress from other co-workers and I work at my own pace.

I worked at a grocery store before and since it’s not a corporate Starbucks(standalone) the rules for clothing and stuff are up to the grocery store. It’s pretty difficult at first, but you start to learn how similar the drinks are with minor differences and it becomes easier to remember drinks. At least a grocery store Starbucks should be slower since there’s no drive thru and all that so it should be less stressful.