Why not one contract per industry? See "Why one contract for every industry" in the root README — category is metadata, not a separate code path.
Can an organizer change the resale cap after tickets are sold?
No — max_resale_multiplier_bps and royalty_bps are set once in
create_event and apply to every ticket under that event for its
lifetime.
What happens to a ticket if the organizer account is compromised? Whoever controls the organizer's signing key can revoke or check in tickets for that event — the contract has no separate recovery path. Treat the organizer key with the same care as any other high-value signing key.
Is there a maximum number of tickets per event?
No hard cap in the contract; tickets_issued is a u64 counter.