Have a look at onstep by Howard Dutton. Its excellent. A few here, including me, have done it.
https://groups.io/g/onstep
http://www.iceinspace.com.au/forum/s...d.php?t=133677
Onstep is arduino/teensy based and works really nicely by itself via Bluetooth with an android app from your phone. Or you can align with the app then use standard apps like stellarium (on a computer) or skysafari (on phone). Take some time to go through the ONSTEP group and there's a lot of helpful people there.
I used NEMA14 steppers on my EQ5 which is supposed to be pushing it a bit, but it works fine. So I imagine they would be fine with an EQ3. Get 400 step/rev ones if you can get them - I got some on au.ebay and even started with 200 step/rev ones which would be fine for visual (probably). I used GT2 pulleys/belts with 2.5:1 and have moved to 3.75:1 (40:16 teeth and 60:16 teeth). Very easy to build up. I made metal holders and used the standard stepper mounts. Now I've just got a 3D printer so will rebuild the holders with this. As far as stepper drivers the TMC2130s are the best around right now - super quiet and expect 1/32 interpolation. With my gears I'm supposedly getting 0.2arcsec per step.