Is it possible? Yes. And you’ve mentioned stability could be an issue. I’ll add that if you count your time and wasted plastics to test the thickness, infill, etc. I think it’ll cost more than just buying the extrusion.

That said, if you already have core xy printer, you can start testing by replacing the frame with a printed parts. Starts with the vertical ones.

1. If micro stepping varies that much then FDM printers (and CNC machines) wouldn’t have worked so well. Also, you can tune the micro steps, if you need 410 steps to move exactly 10mm instead of the default 400, just change it. (I just pull a random number btw, it’s been at least 5 years since I touched my Marlin firmware)
2. If you’re familiar with coffee grinders, they’re basically using thread to adjust distance between 2 burrs. Even there (mid to upper-mid range ones) can’t guarantee the same grind size on the same setting for different unit of the same model, eg. setting 11 on grinder A will have slightly different result compared to another unit of grinder A on setting 11. Can it be done? Yes, one example is Commandante, that is a $300 hand grinder.

Tight tolerances will exponentially skyrocket production cost, period.

It’s extremely expensive to produce things with tight tolerances. Cheap 3D printers have gotten away with it by making things “good enough”. Which why you got this the other way around;

In short, instead of an arbitrary number like 0.3mm that has no meaning to the user, they tell the user to turn this knob 1/4 of a turn. An instruction the user can follow.

0.3mm is easy to measure with the right tool like digital indicator. On the other hand, quarter turn on a knob might adjust 0.3mm on one bolt, but 0.5mm on another.

Also as mentioned, ABL, cheap and can be DIYed. Cheap / printed parts can warped over time, bolts can shaken loose, etc. ABL just put these out of the equation.

Turntable uses needle to feel the “bumps” and turn it into sound, if the needle can feel dusts (which is why people always wipe them before playing), it can definitely feel the layer lines.

Dusts are like what single digit microns? while the best resolution for resin printer is at 10 microns.

I just use the cheapest fruit dehydrator and snips away some of the trays.

What is VSO?

If it’s fine with PLA then my money is on profile issue. Use your PLA profile, and just change the temperature. If that works okay, start tuning for PETG from that point. And delete the old PETG settings.

That looks like it’s not melting fast enough for the extruder speed. Try higher temp, or slow it down, or both.