They will remain in play until banished, although they may require additional Ink cost whenever a player uses the ability unless it is a passive benefit
For Gruul mana-fixing, I recommend prioritizing dual lands that count as both Forests and Mountains: Cinder Glade, Stomping Ground, Sheltered Thicket, and Taiga (if you're willing to spend lots of money) add layers of extra synergy to the deck because they can be fetched by lands (Wooded Foothills) and spells (Wood Elves) while also empowering cards that care about land types like Valakut, the Molten Pinnacle and Howl of the Night Pack
Since youre ideally hitting all your opponents, you can look towards cards that care about that, from the classic Coastal Piracy to cards like Tymna the Weaver and Professional Face-Breaker that explicitly care about damaging each of your opponents
The value of X is determined only once, as Maester Seymour's last ability resolves
Lands, rituals, tutors, draw spells all live again, then get exiled
(Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.) Destroy target creature or planeswalker
