First let me correct your definition of imminence. It does not mean t happen very soon. It means it could happen at any time which still holds true.
First of all, the sense of "imminence" is clearly defined by God's own terms of what an "at hand" prophecy is. ALL of the unsealed prophecies of future events found in Revelation John wrote were "at hand" in Rev. 1:3 and 22:10. God defines this "at hand" term as a prophecy that is first spoken and then performed "in your days" for the ones that the prophecies are spoken to. They are not "prolonged" into "times that are far off". The lengthy discussion by God concerning this kind of "at hand" prophecy is in Ezekiel 12:21-28.
John wrote in both his introduction and conclusion (Rev. 1:3 and 22:10) that his written prophecies of future events were then "at hand". This means that anything written that was related to future events was going to be fulfilled
in John's days - not in our future (they were
not "prolonged" into "times that are far off" to John's days). John was told to write about "things which thou hast seen" (past events) "things that are" (presently occurring back then) and "the things which are
about to be hereafter" (soon to come in John's generation).
You have listed quite a few questions above, and there is a past historical fulfillment for every one of them. I can start with the first two.
1. Give the historic date when the world saw and heard the angel fly around the world warning people against taking th emark.
2. What was/is the mark of the beast that was commanded every one and everywhere to either receive on their right hand or on their forehead
To define the mark giving homage to the Sea Beast you have to first define that Revelation 13 Sea Beast. The Sea Beast had a conglomerate history of lion, bear, and leopard features (Rev. 13:2). These were Daniel's beast empires of Babylonian, Medo-Persian, and Greek empires respectively.
This Sea Beast represented all the pagan world empires which had held control over Israel since Daniel's deportation to Babylon in 607 BC (a 666-YEAR history as of the time John was writing Revelation).
In John's days, the next Roman phase of the Sea Beast was then in place. We know this because Satan, the Dragon's throne in Pergamos was given to that Sea Beast (Rev. 13:2 compared to Rev. 2:13). In real time, the throne in Pergamos was given to the Roman republic in 133 BC by the dying king Attallus III who had no heir but his Roman ally to whom he could pass his Pergamum kingdom. This means the Sea Beast in John's days was in its final Roman phase of existence.
The Judean Land Beast of Rev. 13 became linked with the power of that Rev. 13 Roman phase of the Sea Beast (the Roman "iron" mixed with the miry "clay" of Israel in Daniel's image of a man). Israel was given authority by Rome to operate as an approved "religio licita", as long as the priesthood made a daily offering for the empire and the emperor. "We have no king but Caesar" showed the high priesthood's willing subservience to Rome, and collaboration with them.
In 19 BC, when Herod was about to begin the costly temple renovations, the priesthood asked Rome for permission to start minting their own currency for use in the temple. The Tyrian shekel which had been circulating until then had become debased in its reduced silver content, and the priesthood wanted to have a purer coinage for temple use. Rome agreed to allow this, as long as the priesthood kept using the pagan images and inscriptions found on the original Tyrian shekel. This was a clear violation of God's laws concerning the images of other gods back in Deuteronomy 7:25-26. Yet the priesthood wanted the profits they could make from exchanging other foreign currencies for the Tyrian shekel (the profit collected by the "moneychangers").
No other currency was allowed for temple use or for paying the annual Temple tax by adult males in Israel.
No sales or purchases of sacrificial items for worship could be made without this abominable coin required by the temple priesthood which gave homage to Rome, to the city of Tyre, and Rome's demi-god Herakles. Even the women wore headdresses with a set of these Tyrian shekel coins
on their forehead, to denote their marital status (as in the parable of the "lost coin").
The required use of this coin which gave homage to the Roman phase of the Sea Beast was done away with in AD 66 when the Zealot rebellion cast off their Roman overlords and started minting their own temple currency with a new inscription on them, saying "For the redemption of Zion". Until that time, anyone forced to pay that onerous fee for exchanging their other coinage for the forbidden, abominable Tyrian shekel had no rest day nor night from that forced requirement given by the Judean Land Beast (the religious leadership in Israel) giving homage to the Roman Sea Beast in collaboration with it.
As for the identity of the 3rd "angel" that warned the world against worship of the Sea Beast or the use of the mark, this can be
a human "messenger" and not necessarily a
celestial "angel". I believe these "angel" messengers to be some of the resurrected Matthew 27:52-53 saints who had remained on earth in those days to serve in the early church. The imagery of these "angel" messengers "flying in the midst of heaven" seems to indicate that these are neither celestial nor regular human messengers, but a human messenger in a glorified, resurrected state. The warning given was against participating in the temple worship using the Tyrian shekel, because the AD 66 Jerusalem siege was going to trap within its walls all those coming for temple worship starting in AD 66. The torment of those trapped inhabitants of Jerusalem between AD 66-70 is horrendous by any historical account.