The Templar knights flooded Europe with many fake religious relics during and after the crusades. We do not know if a single one was historical. We have had countless examinations of those relics come back and show us what they are versus what they purport to be. The medieval Church was aware of it. It was a lucrative "business" to drive the pilgrimages. Pray at such relics at your own peril. Many have.You touch on a number of issues that I can address.
1) During the crusades the Templars raided religions sites and liberated many items. What are they? Not my forte. One item was the Ark as the cipher refers to a secret chamber as the one the Ark was stored. In that the depositors were bankers I guess a well documented cache will come with a manifest - a book of the contents.
2) Rick and Marty are not treasure hunters by experience or success. They have no idea what to do. At this point they are not wasting money as its a profit center which allows them infinite failures.
3) Historically civilizations has come and gone and most of what we have is their stone(s). Templars knew this might take 25 generations so they created a written, ritualistic and graphic legacy in FREEMASONRY. The cipher connects this almost conclusively. In their Medieval way. On the level of navigation I am good. On the level of math I had help online. As for who and their politics I am in the dark.
4) The stones tell a story that goes further with Kabbalah - not my thing but its a templar story.
There isn't a single ark. The ark comes to us from Hebrew folk tales inspired by the Egyptian tradition (as does the story of Moses and the Hyksos expulsion out of Egypt). What we now tend to call the ark was known to Egyptians and Israelites as the "barque of Amun". It was housed inside the Temple of Amun and was paraded on religious occasions on poles. Within the barque were the means to locate the placement of the Temples who could not be situated just anywhere (the surveying means to do this were an in-house "secret" that was held by the priest class). There were more than one. There were at least 5. They were used to mirror a celestial geometry that involved the movements of the star Sirius on the Earth.
To get to where one would want to believe that this Templar bullshit is historical requires one to believe in the Judeo Christian folk tales that will never stop being peddled due to their massive popularity in the West still today. There is a long line of fictions one must get on board with to even start to suggest that precious religious relics were transported to Nova Scotia. I can tell you who the people are who can get on board with this suggestion. They are Judeo Christian faithful first. They are probably most interested in finding confirmation of their beliefs. Some of the most committed people to the telling of these Christianized stories are the modern Holy Royal Arch Freemasons who role play the identity of the Christian Templar Knight. These men are not from a direct lineage of anything. The lineage is symbolic only.
It is easy to think one can recognize the details of well known religious stories at OI. That's because the details you are given are meant to do that. The Holy Royal Arch Masons want you to believe in something. That something is not a material treasure. It comes on the other side of death. In life you cannot know. The vault in the shaft is unattainable. You cannot dig to find the answer. Only when the 7th King has died and the Antichrist (the 8th King) has showed up will the treasure be available to ALL. Who believes this nonsense today? The eschaton did not come in 1843 when the second coming did not materialize as so many had wished. OI fizzled. Then it got reinvented in so many ways post 1860. From the 1890s to the the 1930s it was about a search for a vault of Tudor documents. Even Dan Blankenship's partner, David Tobias, was still of the opinion they were chasing documents. Tobias hired real historians and a professional treasure salvage company to study the origin of the OI story. They came back with the result that it was a fiction. No part of the early story can be corroborated. Worse, it can be shown to not have developed as described by the reliable historical record. Tobias took his money and left. Dan stayed and he was forced to rely on dowsing for treasure and the suggestions of an American researcher who had drawn parallels between the OI story and he alchemical quest which was said to be contained in a star map (George Starkey's 1650s pursuit). That's how your star map idea has made its way to be included in various suggestions we still encounter. It is a mish mash of poorly imagine linkages today. But, it still functions as a beacon for mystery story peddlers. It most likely always will.