Negative influence floors at 0. Credits floor at 0 — if you'd lose more than you have, you lose what you have.
Simultaneous effects resolve in priority order: Character Abilities → Follower Abilities → Action Card Effects. Within a priority level, current turn order breaks ties. When an effect causes a new game event (gain credits, gain follower, enter phase), any abilities that trigger on that event get added to the queue and resolved at their own priority.
Ongoing effects — some cards have effects that persist or trigger later ("for the next two turns, gain 2 credits", "during this Engage, gain 1 credit per 6 you roll", etc.). They trigger automatically at the right time.
"When you win this follower" effects see the game state after the follower has joined you — so a "gain 1 VP per Meme follower" trigger counts the new follower itself. The exception is text that says "another" — that explicitly excludes the new follower.