Well, I played the first mission again with my experienced group. The number and/or weight of the opposing forces is definitely impacted by what you bring into the mission.
IIRC, I faced:
First Wave: Wolverine(110T), Jenner(70T), Spider(60T), Centurion(100T), Rifleman(120T)
Second Wave: Stinger(40T), Commando(50T), Warhammer(140T), Phoenix Hawk(110T), Battlemaster(170T), Oscout(70T)
It was a blast. I got low on ammo toward the end (generally I use limited ammo levels because I only face my own tonnage) because there were more targets than my typical quick-combat solo games. Escorts helped with the first group, causing the Spider's engine to blow (which kept the Jenner down and severly damaging the Wolverine and Centurion).
I'm not sure I'll play this campaign again with my experienced group (none of whom have died). I got nervous when I saw both the Warhammer AND Battlemaster emerging from the forest with the 2nd group. Fortunately, their skills seemed low, so I didn't take severe damage.
I should finish the remaining 3025 mechs this weekend and will post them afterwards.