Where do you start when optimising?

I've had a lot of fun trying all sorts of different builds through the game and have never had a 'main' but I'm at the point where I have one char that I play far more than the rest, the fire bowa, and I'm at the point where I'd like to start focusing my modest Wealth on optimising her a bit, rather than spreading it over multiple chars.

My question is, without infinite Wealth to throw around, where do you start? I have an average torch (14/15) and a decent anni (15/20/10). The gear is good but not yet fully optimised. I.e.: I've got a Flickering Flame but after three re-rolls the highest -res I've yet managed is -11; I have a bunch of facets in a 4os armour but a) the facets aren't perfect, and b) the armour is White, BiS would be some sort of jeweler's armour. In terms of charms, I have some plain skillers, a -74 sunder and an average Gheeds, the rest are mainly small res charms. I assume optimum setup would be skillers with FRW or life or fire damage + similar small charms.

In theory: start with optimizing main gear, torch and anni, some skiller GCs, then use other charm slots to cover for what you miss (fhr/frw/mf/life/mana/res...).

Practically: omg there is that xxx sc of xxx for only xxx, I am sure I'll use it on one of my chars, I want it now.

Anyway: start building it on maxroll.gg with the stuff you already have.

Runeword would be the last for me.
Theirs value won't increase by the time as much as unique and charms.
A perfect hoto can't be sold for more than 11

Vex.

For bowazon I generally start with how I plan to play it, in your case fire bowazon.
I get the "main effects" down as you've likely considered with %

Pierce capped, and as much -fire resist / + fire damage.
Then I enhance that with what I call "secondary effects" leech /

Life Tap / open wounds / poison damage / knockback / freeze target etc etc.
Then I move on to getting enough str for the gear used to gain these effects, then for bowazon dex until I've got the damage and/or attack rating I'm looking for.
After I get those worked out and it feels how I want, I move into balancing +skills and +resistances as the final touch.
I usually consider my build evolved when I start looking for skillers to finish it off.

I optimize with whatever I can get my hands on at the time, but I'm staying nearly broke so I have to look for good deals on what I need down the road.