I would agree with much of the sentiments here, you reach for the traditional dug in defensive position vehicles like the LRM Carriers. I would agree with the mechs being the QRF with some hovertanks in support- particularly LRM equipped hovertanks so you can move to where your remaining infantry platoons & squads could be spotting for IDF. But one of the other distinctions would be placing things the RAF had plenty of before Gray Monday- the old slow JES I to be part of the QRF while JES II are dug in as very heavy LRM support for the various lines. The Winston, at 3/5 and with lots of fire support options, goes to the Redoubts while Kinnols go to the field formations. Captured Pixius absolutely go to maneuver formations along with Po tanks & Gauss armed Po II, while the original Po II with UAC/20 is for ambush points in the Redoubts lines or sealing nearby breakthroughs.
Despite being wheeled, I would expect a LOT of Hetzers & Hetzer clones running the range from the LRM version to the AC/20 flavors. You can run the wheeled vehicles from prepared defensive position to prepared defensive position hull down and get more use out of them than you would trying to get over terrain as part of maneuver forces.
Either long range firing vehicles or short range but heavy damage vehicles to seal breakthroughs IMO would be what you assign to the Redoubts.
I also think the infantry gets interesting . . . every single AC/2 or AC/5 you ever mothballed for a rainy day, well brother it is going to be pouring Clanners. Your infantry conscripts get handed all those old autocannons for field gun squads inside bunkers. But, depending on doctrine, I would think the infantry are also the ones manning hull-down trailers- particularly getting emplaced during lulls to replace destroyed bunkers. All the trailers but the "Stronghold" bring serious firepower and offer plenty of artillery options with A4, Sniper, & Thumper systems- heck even mortars.