If you have a way to intentionally ping your own creatures, Silverclad Ferocidons can clear out a lot of the board for you
In my years of personal experience, examining good decklists, and talking to people much smarter than me, 50 mana sources is about the right number for most decks to shoot for, usually 37 lands and 13 ramp sources for a general budget deck
Finally, starter decks come with a single booster pack of 12 random cards
It would be better as a B enchantment that just said "0: Discard a card from your hand." Speed is nice but in the cube things are a little more rounded
Theme Boosters can also contain uncommon showcase cards
10 Ugin's Labyrinth Borderless - $60.74 Lands can be huge players in a deck, helping to accelerate out your biggest spells or helping to keep your game consistent