Charleston has been in serious consideration for several years now so if someone can organize it that seems like probably the best choice. Fort Sumter, Fort Moultrie, Fort Johnson, Fort Lamar / Secessionville, and the Hunley plus the historic town. And maybe the folks from Castle Pinckney could arrange a boat tour?
Atlanta is doable, but will have to be carefully planned to deal with weekday traffic and weekend parking. Fortunately/unfortunately, almost all the surviving stuff is outside the beltway. Marietta to Dalton is about an hour, which is a little longer than typical, but not unreasonable and you'll end up back at the muster hotel in or near Marietta. You could do basically Powell's Volume 1 on Friday, Volume 2 on Saturday, and either Atlanta History Center or Lovejoy's Station (if there's enough of it?) on Sunday.
Kentucky if you base out of Lexington, Perryville and Richmond are both about an hour away and Frankfort is about a half hour. Henry Clay's Ashland is also in Lexington.
New Orleans is going to probably be one of the most expensive Muster locations for a hotel. Baton Rogue is probably too far do as more than a pre/post event side trip.
Red River Campaign is probably too spread out.
For potential revisits, I think the two main candidates would be Chickamauga (it's a complicated battle) or Murfreesboro/Franklin/Nashville (the Muster there was in 2022 and the attendance might have been on the low side due to the pandemic.
Two other ideas:
Jacksonville, Florida: Fort Clinch is an hour away and has Union reenactors on the first weekend of the month and Fernandina Beach has a few Civil War era homes listed on the Florida Civil War Heritage Trail. Yellow Bluff Fort is a short stop for some earthworks. Camp Milton (western outskirts of the metro area) has a little interpretation and Olustee is about a half hour past Milton. The Mandarin Museum has an exhibit about the Maple Leaf which was sunk by a Confederate river mine. Kingsley Plantation is an antebellum slave plantation east of Jacksonville with a rather unique history. Evergreen Cemetery has 250+ Civil War veterans, including J. J. Dickson. Old City Cemetery has another 220+ veteran graves, including Joseph Finegan. Used to be the Museum of Southern History, but that closed last year - apparently permanently.
Savannah: Forts Pulaski, McAllister, and Jackson. An extensive historic downtown. I don't know if any of the Confederate defensive line from 1864 is identifiable? Hilton Head Island is an hour away (Forts Howell and Walker, plus Mitcheville), as is Beaufort in the same direction (including Reconsturction interpretation).