Now, if we took the royal navy example and expand it to work with starfleet's size there is one other element to take into account: The way Federation space is divided up. Now, from the licensed and fan works of the time, they all tend point to a spherical map. With a centered "core" sphere called quadrant 0, with the outer sphere divided up into four quadrants wrapped around the core, called quads 1 - 4. Each of these is divided up into a northern and southern sub-quadrant, with each sub-quadrant being divided up into sectors.
Now, if we follow the royal navy system for line officer commands, one could theorize that each quadrant is under the command of a fleet (5 star) admiral. These admirals would make up "The admiralty" board, with the sector 0 fleet admiral being the most senior and head of starfleet as a whole as well as his quadrant, the "6 star". Under each fleet admiral would be an admiral (4 star) in command of each "sub-quadrant" fleet, which would be the "numbered" fleets, ie 7th fleet, 10th fleet, ect. Flag officers, and Officers of flag rank, serving under the admirals would vary in numbers depend on how many were needed. (Note: A Flag Officer would be anyone commodore and above who is in command of a "fleet element" of three or more ships, where as an Officer of flag rank would be a commodore or above who is serving in a staff/support position, and as such does not command a fleet element.)
Ok, so we have the max number of five star admirals, with the senior as head of the service and of the "admiralty board" as the "six star" admiral. A Positional rank, not an actual one. As such it doesn't carry any rank insignia different from that of a regular fleet admiral, so the pin is the same. The only difference being the added gold stripe on the jacket flap and pants to designate his "senior status" while maintaining the same rank insignia.
Also, aside from the CinC title, one could also say that the formal titles of the senior five star is "Admiral of the Starfleet" while the formal titles of the other five star's would be "Fleet Admiral"
I also have an answer for "colonel west". He, as head of the starfleet marines, may have actually held the title of "Colonel-Commandant" which was the original title of the head of the USMC and a rank title used in the royal marines up until 1913, but continued on as as an honorary or ceremonial title relating to the head of a military corps. As such, he could have held the rank of Vice Admiral/Major general, but as the head of the marines he was the Colonel-Commandant and was referred to by the senior admiralty as "Colonel West". This would make since further if the starfleet marines of the time used naval rankings, as all onscreen evidence shows us, then there would be no colones in starfleet except for west.
Flag officers
1 - Admiral of the Starfleet
4 - Fleet Admiral
9 - Admirals
18 - Vice Admirals
54 - Rear admirals & Commodores
General Staff Flag Officers
Commander Starfleet - Vice admiral to Fleet Admiral
Operational Commanders - Rear Admiral to Admiral
Chief of star fleet Operations
Commander, Galaxy Exploration command
Commander, TACFleet
Commander, Colonial Operations
Commander, Merchent Service
Commandaunt Starfleet marines
Commandaunt starfleet Border Service
Chief of the General Staff - Vice Admiral to fleet admiral
Department Chiefs - Commodore to Admiral
Logistics
Communications
Intelligence
Tactical
Personell
Training
Medical
Shore Establishment