Do all Kamen Rider have a connection to Marvel, DC & Image superheroes?

KR Birth feels like Iron Man

KR Wizard has some Doctor Strange

KR Ghost with Ghost Rider

In what way is Ghost similar to Ghost Rider beyond their names having the word Ghost in them?

No.
Next question.

Trying to use Heat in conjunction with Skull makes a better Ghost Rider. Skull vanilla does that even.

Ghost is more like Danny Phantom if anything.

Has Kuuga (Godai) ever fought against electricity users? I believe Kuuga would be immune to electrical attacks judging from how he unlocked the 'golden power' we know as Rising and Amazing Mighty

Can't seem to remember any iconic ones right off the bat. I do know Amazing Mighty was achieved by Yuusuke temporarily stopping his heart and then get electroshock which triggered it.

You're absolutely right, although you could feasibly do the "Arrogant JERK Main Rider" and still make it work "with the kids". Simply, the Rider starts off as a conceited jerk, doesn't listen to anyone, tries his own way despite his support cast begging him not to but, of course, this road leads to disaster. Consequently, he learns valuable lessons in trust and friendship, becoming a much stronger Rider as a result. Of course, you'd keep aspects of the earlier persona because, let's face it - bad is cool!

I know, which is why I believe he'd be immune to it. It also got Rising

I always thought it was hilarious that Kuuga got form upgrades from a freaking defibrillator. Nothing else is even close to being that strangely mundane.

Also, defibrillators don't restart your heart. So if his heart stopped, he could be struck by lightning and it wouldn't do shit. Humans aren't Frankenstein's monster, after all.