This is a cool topic, but you ruined it by saying exactly what I was going to say.
I'm pretty sure I've written about Balor's debut before. The best place to do it is at the Royal Rumble. Have him come out at number 30. Lights go down. Balor rises out of the smoke in full body paint as his music hits. Announcers freak out. The camera shows him from the front all the way down to the ring, with maybe some shots of the fans freaking out. Then when he's doing his pose on the turnbuckle before getting into the ring, switch to a camera shot from behind, showing that all the wrestlers in the ring have stopped fighting and are just looking at this guy in awe.
I am one of the few people who doesn't think Balor is quite ready for the main roster cos his promos suck and he doesn't have much of a character outside of his paint gimmick. That's actually starting to change lately, which is great, but I think he could use a little more time. So I'd agree that it'd be good to hold off on his full debut until after Wrestlemania. What I think could be cool though is to start a cross-promotional feud between him and a Raw wrestler between the Rumble and Wrestlemania. It'd keep him in the minds of the Raw audience, with sporadic appearances until he was ready to come up to the show for good. I'm thinking he could eliminate someone from the Rumble match, last until near the end and then have the person he eliminated come back to screw him over somehow. A cross promotional feud with Rollins could be cool. Or even Bray Wyatt or Sheamus.
As for Joe, I feel like he could do a lot more than he has done on NXT, but it really depends on where they need him most. Because Joe could walk onto the main roster tomorrow and be one of the most over guys on the roster, but without being too exposed. I was going to suggest the US Championship Open Challenge too, but I think another cool way to introduce him would be in a 'Pick Your Poison' situation. I've always loved the Pick Your Poison gimmick, I'd like to see them bring it back at some point.
For anyone who's unfamiliar with the gimmick given they haven't done it in a while, it's where two participants of a feud both pick mystery opponents for each other to fight on Raw. Usually it'll be a feud between a champion and the #1 contender. It'd be great to see a cocky heel end up having to fight Samoa Joe. Joe comes out, the fans freak out, he goes beast mode on his opponent and picks up a shock win against top level opposition. I'd make sure the gimmick was used in a smarkier town too, so Joe would be recognised by the majority of the fans.