I tend to not do all that well in courses that involve a lot of numbers, so COMMERCE 2FA3 is definitely a bit of a worry for me.

I'm finding Dr. Deaves' textbook incredibly difficult to understand, and feel like I'm not making and ground on the content. For those who have taken this course before, how would you recommend studying so that I can get through the course? Should I ditch the textbook?

Do not ditch the textbook. Try and understand it as much as you can. Leverage the T.A. office hours (not just the week prior to the midterms) since they are a very great resource that goes unused. I ended up with a 10 in the course, primarily due to the T.A.s helping me out.

i did "ok" in this course. prof deaves isn't the best, but i would suggesting doing as many of the problems from the course pack as possible, and like mentioned above, try and understand the book as much as you can.
all the best