Do I need a Hub for my application?

Of the commonly implemented types of Ethernet, only 10-base-5 and 10- base-2 can be arranged in a physical bus. 10-base-T is simply not electrically compatible with that sort of thing (specifically the TX lines from one side connect to the RX lines on the other, and the sender doesn't disconnect, unlike the coaxial PHYs where the sender is only really driving the (single) bus when it's transmitting a packet).

The twisted-pair Ethernet does not work that way. You'll need hubs or switches.

The original coaxial-cable Ethernet worked that way, if the branching and tapping rules were obeyed.

Well, my application needs to support both coaxial-cable and twisted- pair, 10-base-2 and 10-base-5 and 10-base-T. I am thinking about integrating a switch into my device, say the broadcom switch for example, then connect the devices by "daisy-chain". Will it work? Do I need to modify the firmware or everthing will be taken care by the switch automatically?

WTF? Are you working on a method of sending this device through a time machine into 1992? If you are asking this type of question, I highly doubt you are building a device to retrofit into legacy military/ banking operations, and I can think of no other first-world entity likely to have such ancient technology in active service.

Not any more it doesn't. Ethernet is logically a shared medium, but hasn't physically been a bus since effectively forever.

No.

No. For that to work, that "stick" must be, for all intents and purposes, a hub. Or something even more unlike a simple cable than that.

Right. The moon is too high to reach. Well, I am willing to drop off the support for coaxial-cable, let's leave just the twisted-pair here.

Ignoring physical connections for the moments. Your devices still need to have distinct IPs or the very least distinct tcp ports on the same IP.

Probably not, without more work.

Most likely.

Probably not, without DHCP, IP NAT and companies.

Why not use RS-485 sensors and connect the sensors to a RS-485 serial cable and that to some ethernet/RS-485 converter. Of course, there can be only one master (at a time) on the LAN side to poll the sensors one at the time.

Just install an extra double port ethernet interface cards on each PC and use point to point ethernet cables between each machine, with plenty of throughput :-).

That depends on how smart the RS485-Ethernet converter is. You can get converters that understand Modbus and will handle multiple masters on the Ethernet side.