Back to basics.

Ok, first of all, this is my first time posting here. I'm a one man IT department with a modest amount of networking knowledge from being a 25N in the army. The majority of my civilian career however has been managing VMware and Wintel server administration, so please be gentle, I'm by no means a career network pro. I simply know enough to get by (or get in trouble) in small networks. A discussion in a private facebook group for IT folks about the fundamentals of Ethernet had wondering a few things and it was at this point, my brain ran away from me...

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(I'm going to number my questions so if you feel like answering any of them, you can number your answer)

1. What were the origins/applications of "IP Broadcast" in the early days of ethernet?
2. Was broadcast back then "litteral" in terms of literally broadcasting onto the coaxial medium or has it always been protocol based broadcast?
3. What is the purpose of broadcast on the Internet as it is now? (Not in private networks, I get that)
4. To what extent does WiFi implement ethernet? 4/5G?
5. What/if any broadcast traffic is allowed to traverse the internet between or at least internal to ISPs today?
6. Is there any authority that decides what/who is allowed to broadcast or is it just up to companies like Level3 to manage their own infrastructure's means of handling any broadcast traffic?
7. Is digital traffic on coaxial cable from ISPs still modulated onto a carrier frequency or have the means evolved to be purely digital such as in Cat5? My instincts tell me it must still be modulated because the medium must loop for two-way traffic to traverse one wire. Am I wrong?
8. If the above assumption is correct, do cable companies struggle with frequency management on wire? It sounds like the most nightmarish wave theory problem I've ever imagined.
9. Might companies like this broadcast time or hardware events for infrastructure management or route analysis?
10. Also wondering, on an ethernet network, could someone theoretically configure an FPGA to act like an ethernet controller that would accept packets destined for any IP/MAC address?
11. Is placing intentionally non-compliant hardware on the Internet "illegal" in the same sense that the FCC punishes unlicensed radio broadcasters?
12. I understand that with proper network segmentation, only traffic in that network segment could be trapped/interfered with but given a small/unsegmented private network, would this see the same data Wireshark would capture?
13. How much of network infrastructure depends on trusting hosts to behave when it comes to bits on wire?
14. What safeguards exist against hosts designed intentionally against protocol?
15. Is the internet especially vulnerable to "rogue" hardware/infrastructure assets that manipulate traffic on the bit level? Is there any history of hardware based attacks on ethernet?

Of course nobody has to answer any questions, but even if you only answer one question, I'm still grateful.