Αριστοκλή, since you asked....
From my observations, it would be best to have 5 Metropolises/Archdiocese, each with 5-7 diocese within them. This would require 1 Archbishop (President of the Synod), 4 metropolitans, and 27 ruling Bishops, with an auxiliary Bishop as the Chancellor of each Metropolis/Archdiocese, and each diocese would have between 42 and 63 parishes (with the majority being in the 50's). The regular synod would be made up of these 5 metropolitans and 2 bishops from each diocese (on a rotating basis), leaving the number for the Synod at 15 (odd numbers are good) with 8 required for a quorum (higher numbers are good).
Just as a preliminary idea, I had divided the Metropolises thusly:
Archdiocese of New York (President of the Synod) - covering the Northeast
Archbishop of New York, Bishops of Albany, Buffalo, Trenton, Boston, Worcester, and Hartford.
Metropolis of Atlanta - covering the South
Metropolitan of Atlanta, Bishops of Miami, Raleigh, Houston, and Birmingham.
Metropolis of Washington - covering PA-OH-WV-MD-DC-DE
Metropolitan of Washington, Bishops of Scranton, Philadelphia, Pittsburgh, Charleston, Cleveland, and Cincinnati.
Metropolis of Chicago - covering the Midwest
Metropolitan of Chicago, Bishops of Springfield, Detroit, Lansing, St. Paul, and Kansas City.
Metropolis of San Francisco - covering the West
Metropolitan of San Francisco, Bishops of Los Angeles, San Diego, Portland, Ankorage, Juneau, and Denver.
So how did I come up with these divisions? I first totaled the Orthodox Churches by state. (FYI: Top 5 - PA: 221, NY: 153, CA: 141, OH: 98, AK: 94). Then I divided them into geographic regions. I then tried my best to align the regional divisions to divide the metropolises as evenly as possible, taking into account those regions which cover more space, and thus should have fewer parishes. When I did this, I came up with the following divisions:
West - 365 parishes, 7 diocese, 13 states, 1,864,361 square miles, 69 million Overall Population.
South - 272 parishes, 5 diocese, 12 states, 810,836 square miles, 97 million Overall Population.
Ohio Valley - 368 parishes, 7 diocese, 6 states, 129,546 square miles, 33 million Overall Population.
Northeast - 372 parishes, 7 diocese, 8 states, 135,194 square miles, 42 million Overall Population.
Midwest - 289 parishes, 6 diocese, 12 states, 846,947 square miles, 58 million Overall Population.
It should be noted that the Ohio Valley and Northeast combined have 25% of the US population, 7% of its land mass, but 44.4% of its Orthodox parishes.
Once I had divided the country regionally, I then proceeded to divide the regions into diocese, attempting to keep around 50-55 parishes in each (in order to sustain the expenses of the Diocese), while also trying to have diocesan borders not cross state lines (in some areas this was quite easy, in others not as much) or to engulf multiple whole states versus 1 and 1/2 or 3 and 1/3.
Certain states with a very large number of parishes in them are large enough to have one or more diocese perfectly maintained within their state boundaries. These are: PA, NY, CA, OH, AK, IL, FL, NJ, MA, MI, TX, and CT.
After dividing the states into diocese, I then attempted to chose major cities with large Orthodox populations to be the Metropolitan centers, while also trying to keep the Metropolitan centers close to the center of the Metropolis (the exception: Washington, which is on the edge of that metropolis). And after that, I attempted to chose other smaller cities with significant Orthodox populations that are/were centered on their diocesan area to be diocesan sees.
In addition to the 5 metropolitan/archbishops, 27 ruling bishops, and 5 auxiliary bishop chancellors, I also accounted for 5 other Auxiliary bishops: 1 to oversee Overseas Mission (OCMC/IOCC), 1 to oversee Domestic Missions, 1 to direct Communication, and 2 to be the Presidents of Seminaries - one on the East Coast, and 1 on the West Coast. Each of these 5 Auxiliaries would have their offices spread throughout the country: the IOCC/OCMC Bishop would be in Baltimore (Ohio Valley Metropolis), Domestic Missions in the South, Publications in the Midwest, and the Seminary Bishops in the Northeast and West. Thus, with their services also available, each Metropolis would have between 7 and 9 hierarchs in their area to serve between 270 and 370 parishes.
This is of course a preliminary survey, using information from the SCOBA website (directory), as well as US census and geographical information.