Is it possible to play without mixed ore patches?

Yes! Check the mod settings.
Pie-chart ores: Disable Mixed Starting Resources and/or Mixed Resources.
Single ore type per hex: Set Resource Bias to 100.
Through gameplay: A Fulgora quest unlocks the ability to unmix ores.

Does this mod generate hexes and hex cores for modded planets?

Not until integrations are added. It is specifically designed and balanced around vanilla DLC planets.

What vanilla weapons does this mod buff?

Discharge defense, teslagun, destroyer robots. Each now function as tesla turrets.
Also defenders and distractors for range and damage, slightly.
Also there's a higher tier of bullets, railguns, and spidertrons if you really need some capable weapons for clearing dungeons.

What can be done with the command /export-item-values?

While it was designed in parallel with /import-item-values, you can upload the file it generates to the HIVE to explore the exhaustive list of item values for every planet, as well as the derivation paths that gave them their values!

Has anyone already made a script to find trading loops in the exported trades JSON?

Yes, I wrote a simple browser-based tool for this!