My goal is to make editable every data within Templates.BIN, ARMOUR.BIN, SPEED.BIN and BUILEXP.BIN, so everything you mention. This is huge load of work to do, but hopefully we'll get there. Buildings and units are the most complicated forms, the others should be easier, I hope.
Did not try that, so no idea, sorry.
Yes, my editor will allow you select whatever building art, even those unused Harkonnen and Ordos turret and barrel sprite sets. It's actually a limitation of TibEd it doesn't allow you to select them. So you will be able to select up to 6 different turret and barrel sprite sets, meaning 6 different turret types without adding new image entries into DATA.R16. Same applies to Repair Pad and IX Research Centre building art.