Thanks for reaching out! The mechanic for the arrows are based off of the Occult Herbmaster in the core rule book, so you can mirror your rulings from there if so.
To be a bit more specific, you would roll a d8 twice each day (re-rolling duplicates), and can imbue d4 arrows, one single arrow not being double imbued.
There's wiggle room for shenanigans in the rules as written, but I leave it to you and your table!