With these upgrades, the deck now has a stronger focus
This mana can only be used to cast creature spells, but in Mono-Green that's likely what you want to be doing anyway
You can feel free to mulligan a hand with three removal spells against a control player who hardly has any creatures
Since you're in green, however, you'll likely have access to plenty of mana, oftentimes enough to pay the cost of Summoner's Pact and cast whatever creature you grabbed from your library
The part where the player loses half of their life isn't instead of the number of objects they chose, but according to the wording, it's actually in addition to the number of objects they chose
Green Creatures Clifftop Lookout: Have you ever had to choose between casting a ramp spell and playing a creature to the board