Will season characters move to eternal realm after the season is over but without the malignant hearts etc?
Yes, everything goes to your eternal realm stash, should include all the legendaries you find as well.
Yes. All Seasonal characters are moved to Eternal
They didn’t mention if you have increased character slots though, but usually you do.
So your char moves to eternal and they just strip off all the hearts and turn the gem slots to normal I’m guessing?
You keep everything from season 1. Everything goes to Eternal including whatever the season mechanic is. Once there you can use your season 1 stuff but season 1 event will be over so you won’t be able to collect more hearts on Eternal.
Blizzard said some season mechanics may find themselves in the Eternal realm but they didn’t want it to be like PoE, where almost every seasonal mechanic is in the game all the time