Note - not a GM (yet)
1. Stuffer Shack on the corner
The rulebook explicitly lists Stuffer Shacks as almost always having their own individual host. Let's say the shack has one security camera, and a solid metal "bandit barrier" that can be lowered upon button press.
I'd have a rating 3-4 Host (low end commercial), to save complexity I'd slave the camera and barrier to it. It'd run Patrol IC, and be able to release Blaster IC and Track IC. Anything Patrol IC picked up would be relayed to head office, but they'd probably have slow response.
2. Commuter train
The train has an engine car in the front, and wirelessly lockable doors. The engine car can be rigged into. Additionally, each car has cameras that are viewable in the engine car.
I'd slave the doors to the engine car, and have it normally rigged. Don't see a need to be a host.
3. Auction company's host (purely in the Matrix, no physical component)
The host contains data on ongoing auctions, and has the ability to send messages to their partner company to ship goods that were auctioned off.
Probably host rating 5-6 if it handles the logistics of the auction including who wins and shipping. Depending on the level of goods, I'd have the IC be deadly or stun. If very high value, they might well have a decker on call.
4. Typical office building
There are cameras around the building, and a security office that can view those cameras. There is a director's office that has private data on his computer. There is a cubicle "farm" with many terminals where employees come in everyday to work. They have to access the same shared data.
Low security would be a host 3-4 with cameras slaved to the host which stores the data, IC probably doing stun. Director computer would be a higher rating device, and not slaved to the host.
Higher security would be host 5-6, cameras either slaved to a security host or standalone, with decker on duty with marks on camera and hosts. IC doing stun or deadly depending on policy.
At higher security still you can add turrets with a rigger, etc !