Instead of Talismans and Signets I'd recommend running equipment ramp Sword of the Animist, Dowsing Dagger, Sword of Forge and Frontier, Sword of Hearth and Home, they are slower but they provide far more value over the course of the game
The strongest Dragons are within Temur colors, letting you play all the best ones, and if Miirym is on the battlefield, even lets you get more than one copy of them.
If you're already in another dungeon when you would venture into the Undercity, you will instead progress to the next room in your current dungeon rather than enter the Undercity as an additional dungeon or switch altogether
The plotting wont matter as much until that specific ability returns, but casting from exile
You can find our upgrade guides for Legends Legacy and Painbow here
Maybe pick up one of the far cheaper, non-full-art versions though