I had a chance to do some testing, and it seems like Zelda's dash grab outranges dash attack very slightly (her grab range is the same as DDD and Charizard's, and longer if you pivot grab). It comes out on frame 10 for dash grab and 11 for standing, IIRC. Upsmash comes out on 6, and dash attack on 7.
Upsmash oos is a good punisher against aerial approaches. A jump canceled up smash will come out faster than anything she can do that isn't a sidestep/roll or jump.
Dash attacks can be used to punish retreating aerials before they can touch the ground (Marth's fair), since it covers a wide horizontal area.
Shield grab can work defensively, but the starup can be problematic against auto-canceled aerials on characters who have quick ground options (Peach's fair to jab).
Offensively, grab and up smash mixups are the way to go.
Starting off by grabbing will let them know early on that they're not safe in their shields. Down throw can be followed up in a number of ways depending on DI, but aside from an aerial that'll likely be air dodged, a grab, up smash, or shield (if they try to attack) are the best ways to cover their options.
When they start sidestepping to avoid grabs, up smashes will cover you. It's a fast attack so it will cover you at close range if they decide to do something offensive that's slower than your attack, or if they jump.
personally, a lot of my dash attack use would be better off being grabs. Best uses for dash attak off the top of my head is punishing or trading with aerials when it needs to be done as quickly as possible. I feel it's especially useful against Marth since he DIs out of upsmash fairly easily if he's already air born and... the dash attack dash attack spike thing if someone forgets they should shield these things.