I'd go back to the original numbering on JSoA so that instead of issue #39, it would be issue #300. Here are the teams I'd have debut that month:

The Justice League of America: Aquaman (Arthur Joseph Curry), Atom (Ray Palmer), Batwoman (Kate Kane), Black Canary (Dinah Lance), Blue Beetle (Jaime Reyes), Bombshell (Amy Allen), Booster Gold (Michael Carter), Congorilla, Doctor Fate (Kent V. Nelson), Doctor Light (Kimiyo Hoshi), Fire (Beatriz da Costa), Firestorm (Jason Rusch), Flash (Barry Allen), Green Arrow (Oliver Queen), Green Lantern (Guy Gardner), Green Lantern (Hal Jordan), Green Lantern (John Stewart), Hawkgirl (Kendra Saunders), Hawkman (Carter Hall), Ice (Tora Olafsdotter), Miss Martian (Megan Morse/ M'gann M'orzz), Mister Miracle (Shilo Norman), Moon Maiden (Laura Klein), Phantom Stranger, Plastic Man (Patrick O'Brien), Red Tornado (John Smith/ Ulthoon), Rocket Red (Maks Chazov), Shazam (Freddy Freeman), Starman (Mikaal Tomas), Supergirl (Linda Lang/ Kara Zor-El), Wonder Man (Achilles), and Zatanna (Zatanna Zatara).

The Justice Society of America: Adam Strange, Amazing-Man (Markus Clay), Black Condor (John Trujillo), Bulleteer (Alix Harrower), The Chief (Dr. Niles Caulder), Doctor Mid-Nite (Pieter Cross), Doll Man (Lester Colt), Elasti-Girl (Rita Farr), Firebrand (Andre Twist), Flash (Jay Garrick), Green Lantern (Alan Scott), Guardian (clone of Jim Harper), Human Bomb (Andy Franklin), King Chimera, Lady Blackhawk (Zinda Blake), Magog (David Reid), Mento (Steve Dayton), Miss America (Joan Dale), Mister America (Jeffrey Graves), Mister Terrific (Michael Holt), Negative Man (Larry Trainor), Phantom Lady (Stormy Knight), The Ray (Ray Terrill), Red Bee (Jenna Raleigh), Robotman (Cliff Steele), Sargon (David Sargent), Starman (Thom Kallor), Spectre (Crispus Allen), Superman (Clark Kent/ Kal-El), Uncle Sam, Wildcat (Ted Grant), and Wonder Woman (Diana Prince/ Princess Diana).

The Outsiders: Atom (Ryan Choi), Black Lightning (Jefferson Pierce), Bronze Tiger (Ben Turner), Captain Boomerang (Owen Mercer), Coldcast (Nathan Jones), Connor Hawke, The Creeper (Jack Ryder), Crimson Avenger (Jill Carlyle), Faust (Sebastian Faust), Geo-Force (Brion Markov), Grace (Grace Choi), Gypsy (Cindy Reynolds), Halo (Gabrielle Doe), Kasumi (Cassandra Cain), Katana (Tatsu Yamashiro), Looker (Emily Briggs), Major Disaster (Paul Booker), Manhunter (Kate Spencer), Manitou Dawn, Menagerie (Sonja), Metamorpho (Rex Mason), Naif al-Sheikh, Onyx (Onyx Adams), Owlman (Roy Raymond, Jr.), Reverb (Armando Ramone), Sister Superior (Vera Lynn Black), Spoiler (Stephanie Brown), Steel (John Henry Irons), Thunder (Anissa Pierce), Vigilante (Joe Flynn), Vixen (Mari Jiwe McCabe), and Wild Dog (Jack Wheeler).

The Titans: Aquagirl (Lorena Marquez), Argent (Toni Monetti), Atom Smasher (Albert Rothstein), Batgirl (Bette Kane), Batman (Dick Grayson), Beast Boy (Gar Logan), Bumblebee (Karen Beecher-Duncan), Cyborg (Vic Stone), Dove (Dawn Granger), Firehawk (Lorraine Reilly), Flamebird (Thara Ak-Var), Flash (Wally West), Green Lantern (Kyle Rayner), Hawk (Holly Granger), Hawkboy (Charley parker/ Ch'al Andar), Hourman (Rick Tyler), Huntress (Helena Bertinelli), Liberty Belle (Jesse Chambers Tyler), Mirage (Miriam Delgado), Nightwing (Chris Kent/ Lor-Zod), Northwind (Norda Cantrell), Obsidian (Todd Rice), Power Girl (Karen Starr/ Kara Zor-L), Raven (Rachel Roth), Red Arrow (Roy Harper), Red Star (Leonid Kovar), Sandman (Sanderson Hawkins), Starfire (Koriand'r), Tempest (Garth), Terra (Atlee), Troia (Donna Troy), and Vox (Malcolm Duncan).

The Teen Titans: Aqualad (Lagoon Boy), Brahma (Cal Usjak), Empress (Anita Fite), Fringe, Hero (Hero Cruz), Hot Spot (Isaiah Crockett), Inferno (Sandy Anderson), Kid Eternity, Kid Flash (Bart Allen), Little Barda, Loser (Theo Storm), Mas y Menos, Maximum (Max Williams), Offspring (Luke O'Brien), Outburst (Mitch Anderson), Prysm (Audrey Spears), Pyrogen (Claudio Tielli), Ravager (Rose Wilson Worth), Red Devil (Eddie Bloomberg), Red Robin (Tim Drake), Robin (Damian Wayne), Son of Vulcan (Miguel Devante), Speedy (Mia Dearden), Static (Virgil Hawkins), Superboy (Connor Kent/ Kon-El), Toyman (Hiro Okamura), White Lotus (Nona Lin-Baker), Wonder Girl (Cassie Sandsmark), The Wonder Twins (Zan & Jayna), and Zatara (Zachary Zatara).

Young Justice: All-American Kid, Allure (Damara Sinclaire), Amazing Woman (Erik/Erika Storn), Blindside (Tyson Gilford), Citizen Steel (Nate Heywood), Cyclone (Maxine Hunkel), Damage (Grant Emerson), Empathy (Lucia), Faith, Fast Forward (Ted Bruder), Fever (Shyleen Lao), Freak (Ava), Girl 13 (Traci Thirteen), Hardrock (Ross Richman), Houston (Joel Weinberg), Jakeem Thunder (Jakeem Williams), Judomaster (Sonia Sato), Kid Slick (Vic Darge), Lightning (Jennifer Pierce), Misfit (Charolette Gage-Radcliffe), Omni (Cameron Begay), Power Boy (Jonathan Kent/ Mon-El), Shining Knight (Justina Arthur/ Ystina), Sparx (Donna Carol Force), Stargirl (Courtney Whitmore), Sweet 16, Talon, Teen Lantern (Terry Berg), Temper (Aviva Weinberg), Vaporlock (Natasha Irons), Wildcat (Tom Bronson), and Young Frankenstein.