[X] Ask Slughorn if he has some books he recommends
Miyuki would be my runner up choice but I am not sure if she is A. Good with potions and B. an old enough student to ask this question. What year is she? I am sure she will still give good advice but I think she is more likely to semi-mock Shinji again for taking a stranger's words at face value (this time scribbles in a book non the less) rather than being skeptical.
I want to not piss off Slughorn this go around and benfit from him this time. At least until Zouken tells us to befriend Assissin Lockhart. Slughorn points are always good here. He is a teacher, its his job to guide people to shape their learning. Asking him for help on a jump off point to see about how alternative recipes work is not cheating. In fact, he likely to respond really well if he finds out that they are going further than the normal but wondering about if this potion receipt is really the best way to go about it.
The man is looking for who in the classes has the talent for him to favor. The person that thinks to go beyond what the potion book tells you is the kind of person that will go father as they have what it takes to be a potion brewer/researcher.