Zombicide: Green Horde

Yes — opening a closed building for the first time reveals the whole building: you indicate each Zone in the building (in any order) and draw a Zombie card for each Zone, placing the indicated Zombies immediately (if an “Enter the Horde” card is drawn the Horde also spawns and the spawn ends). (p. 22)

No diagonal sight or movement on streets; on streets LOS runs in straight lines and can extend across many street Zones, but inside a building LOS only reaches Zones that share an opening and only 1 Zone deep. Ranged attacks follow those Lines of Sight and weapon Range limits. (pp. 10–11, 34)

Yes — missed Ranged, Magic or Siege attacks aimed at a Zone containing Survivors automatically become Friendly Fire and are assigned to Survivors in that Zone (Armor rolls may cancel hits 1-for-1); Friendly Fire does not apply to Melee. (p. 35)

Whenever a Zombie card with the Horde symbol is drawn to spawn, set aside one extra miniature of that type into the Horde; Necromancer cards add a Walker+Runner+Fatty to the Horde; when an “Enter the Horde!” card is drawn the entire Horde is placed in the indicated Zone and the Spawn Step ends. (pp. 19–20, 29)

A Survivor has 2 Hand slots, 1 Body slot and 5 Backpack slots (Hand-only cards must be in Hands to be used). A Body item can make it effectively three equipped items, but you may only use any two of them at a time — choose which two before resolving Actions or rolls; Dual-wielding rules and bonuses apply as described. (p. 17, p. 33)