@ucbalumnus Alright, done and done!
That is, I asked my advisor and she was very helpful.
TL;DR:
Spring: s303
Next Fall: s403, some other 400-level class (s463, m453, s415, etc.)
Next Spring: s404, s312
Here’s the full story: s312 won’t work with my high school schedule, so I’ll have to put it off until senior year. However, honors linear algebra is occupying s311’s super convenient timeslot! I was worried it wouldn’t have extra content (and a bit sad to be leaving my professor) but my advisor assured me the professor was nice and would probably give students with more background extra stuff to chew on. So, that’s that! Not to mention doing so ets me take s403 without any red tape. 
I can even finish up vector calculus with my friends currently in Calc BC! Definitely a net gain. 
s463 (honors probability theory I) is supposed to be one of the easier 400 levels, but it’s also a meaty class and good background for grad courses.
s403/404 are actually somewhat notorious, but they’re supposed to follow pretty naturally from s303. Same for 413/14 and 312 respectively, but I was more excited about algebra anyway haha.
I do plan to ask the linear algebra guy and my current prof. on the differences between s303 and s311! I’ll even show the former our new textbook (the math advisor was pretty surprised by all the linear algebra in there)!