It has been a long time. :)
I thought I would try here to write down what I know so far about getting set up as an actual Civilisation in the Galactic Milieu.
Right off the bat I can tell you that it is not something you can necessarily do "step by step", because in order to be a Civilisation you have to have at least X-number of shares of General Hosting Corp but those shares can only be held by Civilisations.
So there will come a point where you have to have the whole "become a civilisation" thing down pat ready to go and execute it on one fell swoop, getting your share(s) and becoming a civilisation "simultaneously".
The price of the shares should usually be the value shown in the latest Latest Rates include-file; General Hosting Corp shares are the sGHC entry in that file; the values shown by default are denominated in DeVCoins, but of course a large part of the purpose of that file is you can use it in scripts to convert values to and from any of the assets shown.
The reason I wrote X-number as the number of shares required is that although technically you can be down to only one such share and still qualify as still being a Civilisation, the number of your shares you choose to associate with a given planet limits your choices of initial planet.
This is possibly a little "up in the air" right now, and might even vary from planet-offering to planet-offering, but in essence the larger the planet being offered the larger the number of such shares each civilisation wanting to start there must have in order to qualify to start there.
The Latest Rates valuation of your Civilisation's GHC shares is counted as part of its "official treasury", and also serves as "collateral" for any debts it incurs to the General Hosting Corp such as its monthly "per square mile that FreeCiv reports the Civilisation as controlling" hosting fee, which at the start of each month is added to its debt. Basically all fees payed to GHC are paid in the form of loan payments against that accumulating debt, the Civilisation's "hosting tab" as it were.
As is perhaps typical with collateral-backed loans, when the debt exceeds half the total value of the collateral liquidation takes place to bring the total debt down to or below half the value of the remaining collateral.
Thus from time to time GHC might come into possession of some of its own shares, which of course would be held in a slush fund since one's own shares are not supposed to be placed in one's own "official treasury" (because that would lead to an infinite-regress when the total value of the "official treasury" is calculated or re-calculated).
An interesting thing about Civilisations though is that it might be possible to be a "Civilisation in exile", which maybe could be a little akin to something along the lines of being a Minor House in something like the Dune Mythos that still holds political capital (represented by its shares of GHC).
This came up due to the presence on the Galactic Diplomacy Planet (on the CrossCiv.Knotwork.com Crossfire RPG server) of Italians, the player(s) of whom have a goal of being somehow survivors or somesuch of the Italian Civilisation of the planet known as E29.
If you have played the Battle for Wesnoth campaign "Mutiny in 1626" you might have encountered an Italian in there, or at least a character "from Italy" even if not born Italian: Nick La Tess (a wordplay, of course, on Nick Tesla).
Apparently at the time depicted in that campaign, the Italian Civilisation of that planet was down to just one city left, with the Egyptians poised to wipe them off the FreeCiv-scale map.
Basically events there, back then, on that timeline, constitute a "temporal nexus" that has yet to be resolved.
The Italian I interviewed on the Galactic Diplomacy Planet did not know whether or not those E29 Italians would have had to build a Diplomat or Spy unit that got somehow evacuated from the planet, or whether a change of scale could be invoked to explain "survivors" having somehow reached the Galactic Diplomacy Planet.
What was known though was that the Egyptians did not acquire those Italians' shares of GHC by wiping that Civilisation off the map.
Until that Nexus is resolved though it will not really be known whether that Italian Civilisation was in fact wiped off the map at all, since part of why it is a Nexus involves the timelines of other planets that had not reached that date yet thus might possibly, who knows, be able to get fast enough starships deployed in time to get there in time to intervene...