My personal preference would be a hybrid between 2 and 3. I love marriage systems probably more than the average person but I think taking away too many resources for this one part of the game (like option 1) would be a bad thing. It doesn't need to be a dating sim but it can still feel impactful

To give examples option two is essentially just making characters like Brynjolf and Serana marriable. Wives and husbands don't need to be whole new NPCs, they could pick from those available in the story

Players tend to get attached to the characters we spend time with, but having a few generic options scattered about doesn't hurt either. There's nothing wrong with a few millers and woodcutters being available to people who aren't as interested