in my opinion, definitely do what you can on the rust. i used a conical wire wheel on a drill.
even if you don't get every speck of rust, it prepares the surface for paint.
i clean the ash (and entire stove, flue and combustion motor blades) at the end of each season. then paint and place the damp rid holder and packet inside the firebox.
my first season i didn't use damp rid. and i got rust from humidity even through the pam spray coating i used.
this year i just painted with brush on high heat stove black" paint. (just personal preference over spray paint. many people use spray though)
and used the damp rid. zero rust even on the unpainted bare metal baffle plates i put inside after using the wire wheel on them.
if i'm reading your post correctly, you had ash in there all summer?
one guy here posts that he does it that way and has no rust.
but i have no idea how he manages that. i was emptying out water from the damp rid container all summer.
most accepted wisdom is to do a complete cleaning and take rust prevention steps after the end of burn season.
this year i read at least a few people's posts saying they did the cleaning just before starting burning again though.
i wouldn't do that. i know i'd have major rust if i did.
and the fact that you have "a lot of" rust shows you should probably do the cleaning at the end of burn season as well.
here's a recent thread with many views on the topic-
https://www.hearth.com/talk/threads/painting-the-firebox.113387/
