Well Ice I did a little research for this challenge based on your design (found on Solaris 7, link below) and the overview I wrote for Naval Organization in Technical Readout 2800 (PDF page 13).
http://solaris7.com/TRO/Spaceship/ShipInfo.asp?ID=871Richelieu class is a true Battlecruiser with better than average speed (4/6) and good long range capital arsenal. I want to create a focal point around your warship so the partners will hopefully compliment it well. The ships I want to pair her with are just as fast and support various operations.
Now I got three ways to go for organization (see TRO2800). The "Base Three" Squadron (3 warships), the "Plus One" Squadron (4 warships), or the "Dual" Squadron (6 warships).
Furthermore I envision the Richelieu as leading fast heavy hitter group so no corvettes. Not enough punch. Also since the Battlecruiser is heading up the group no Battleships, don't want to overshadow. No non combatants are suggested either I want true warships not tenders, yardships, tankers, or transports. They need not apply. Finally SL era designs only are herein included, no design produced after the Amaris Coup. I included BTSD (TRO2800), Knightmare's Devonshire Historical Archives, and canon sources (TRO 3057 Revised). So here are my potential candidates.
Whirlwind class Destroyer (520k tons / 4,6 / 0 DS / 0 Fs / 0 SC) TRO 3057R
Riga class Destroyer/Carrier (600k tons / 4,6 / 2 DS / 36 Fs / 6 SC) TRO 3057R+
Dewey class Destroyer (600k tons / 4,6 / 0 DS / 18 Fs / 4 SC) TRO2800
Bainbridge class Destroyer (620k tons / 5,8 / 0 DS / 12 Fs / 6 SC) TRO2800
Jocasta class Destroyer (640k tons / 4,6 / 1 DS / 12 Fs / 2 SC) Devonshire / Knightmare
Lola III class Destroyer (680k tons / 4,6 / 0 DS / 6 Fs / 4 SC) TRO 3057R
Kimagure class Pursuit Cruiser (780k tons / 5,8 / 2 DS / 12 Fs / 0 SC) TRO 3057R
Defender class Cruiser (650k tons / 4,6 / 2 DS / 0 Fs / 0 SC) TRO2800
Sovremenyy class Battlecruiser (830k tons / 5,8 / 4 DS / 18 Fs / 8 SC) TRO2800
So from that list let me make my first suggestions to reach a "Base Three" Squadron. Even though the Richelieu and the Sovremenyy aren't in the BTSD setting per say they would make a nasty duo if teamed together. In their fluff neither ship was produced in numbers but paired together as friendly competitors I think they'd do nicely. Next I'd take your pick of the Defender whose AA capabilities would nicely shield the dynamic duo or the Kimagure whose speed and armament make a nice fit. Those 4 ships would also make a nice "Plus One" Squadron.
Now if we go to a "Dual" (6 ship) Squadron I'd likely add in the standard Tin Can Escort headed up by a Lola III and your pick of my other Destroyer candidates. My dream pick would be to keep the original four ships (Richelieu, Sovremenyy, Defender, Kimagure) and add 2 Bainbridges. That would give you really good speed as most of your ships go 5,8 with the Defender and Richelieu doing a respectable 4,6. So what do you think?
