There are plenty of amazing Un-cards to add to your Cube and these are some of the best
You can't wait and play them later
You could even run a small Teshar, Ancestors Apostle loop package to allow you to go infinite if needed, but cards like Scrap Trawler and Teshar are perfectly fine by themselves here, too
After all, Sapling of Colfenor is one of the most-played cards in a Doran the Siege Tower deck, the previous toughness-matters Commander in Abzan colors
When the humanoid races arose, the dragons were at first angered that mortals would try to harness the wild forces of magic, but they came to realize that only through disciplined study would magic be in safe hands
Id add the Cavalier of Flame and Sprouting Goblin, just to have some extra burn and draw, plus the haste enabling from the Cavalier could help end the game