I don't agree with the above assessment that tesla turrets should not be effective against the local threats. In fact, I think it should be one of the more effective weapons, possibly transforming it's current slow-effect into a stun-effect outright. I think this would be in-line with Gleba's enemies, against whom rocket turrets are the weapon of choice, and that is the local unlock there too. Of course combined arms will always be more effective, just like Pentapods are best dealt with an abundance of rocket turrets, some gun turrets to deal with the swarms of the smaller enemies and (luxury item) the odd tesla tower to slow down the big pentapods, so too the fulgoran enemies could be designed in such a way to be optimally fought off by a combination of weapons. In my opinion, a 90-95% fire resistance should be a given, a 50-60% damage reduction from lightning, but at exchange of lightning causing a stun effect rather than a slow might be a good baseline. And I think flame resistance is a very big necessity given that heavy oil is so readily available, and also thematically burning the robots should not be a very effective approach.
I agree that making them moderately resistant to laser and physical and weak to explosive is a good idea. Since they are ranged enemies, explosive rocket might be useful for them (which are totally impossible to use on Gleba due to friendly fire), the local turret offers great defense via the stun but gun/laser turrets still work, albeit not terribly effective, for people that don't want to make it too complex.
As for target priority, the bots seem to want scrap to replicate, so miners being the target of choice makes sense, as they deprive bots of their means to replicate. Either scripting attacks on miners or adding a fulgora-specific pollution type to all kinds of miners would work well and stay in line with what you intend for the enemies lore-wise.