That’s a lot of mechs!
Clans: The most I’d paint up for any one clan is a front-line trinary, a second-line trinary, and any number of Elementals.
Some of the more prestigious garrison forces, like the Diamond Sharks’ Spina galaxies or their Omega galaxy, had omnimech command stars so you could do a 5/10 omni/second-line mix. The less prestigious ones, like a lot of provisional garrison clusters or solahma units, would mix in SLDF or salvaged IS mechs instead. The Diamond Sharks’ Omega galaxy had a great story at Tukayyid, so I’m doing a trinary with a few omnis in the command star. Might swap the Crossbow with the Hunchback IIC because the former was often used in second-line units and the latter sometimes in frontline units – and there aren’t any heavies in the second-line packs (why not??).
A Smoke Jaguar force defending Huntress would be very cool, too. No shortage of canonical opponents! That’d also be the most lore-friendly way to use the Stone Rhino. But then you’d be painting up mechs for two dead clans, and that feels a little limiting. It might make more sense to pick one dead clan (sounds like Blood Spirits for you) and one of the three prominent invader clans that stick around for a long time without totally changing their color schemes (i.e. not Diamond Shark/Sea Fox). Or the Blood Spirits’ opponents. Tough call. The Blood Spirits seem difficult to use.
Inner Sphere:
Using something like Operation Bulldog as a filter is a possibility. Imagine showing off several dozen mechs and pointing out that they all fought together in a single operation.
If you have a favorite invading clan, find the Comstar divisions that faced them on Tukayyid, in the Tukayyid sourcebook, and then find out on Sarna which of those did the most fighting afterward. I’m going with the 85th Div. (8th army) because they fought the Diamond Sharks and then participated in Operation Bulldog. They all use an all-white parade scheme, so unless you’re getting unit decals it doesn’t really matter.
Or give them to a high-end Combine unit (e.g. that 2nd Sword of Light unit you’re considering), or to a low-end clan unit, or just divide them up as rare SLDF remainders in random armies. The Sword of Light is a great choice because they got a lot of the fancier Comstar mechs and they’ll take fewer steps to paint. Red’s harder to paint than cool colors (easier than yellow or white, though), but you don’t have to paint blocks of other colors, just details. With so many mechs to work on, that’ll matter.
I like the Legion of Vega, too. They were at Luthien and in Operation Bulldog.
The Blood Spirits fought the Genyosha at some point, but they’ve got an awfully dull color scheme.