I've been playing this game a lot (1000+ hours according to Steam) and I have found this particular FP to be the most difficult by far. I only played this for he first time just a week ago on an iron man save, 2000 days in, 5 parts for mechs and Loss on CT destruction on. I also have extended sight (400) and sensor ranges(500) which probably helped the AI more than me in the first and last missions.
You should note that I consider a mission a failure should I lose a mech and generally try to kill everything whilst doing so.
This FP has been costly to say the least. Here is a brief Run down of my experience.
Enter FP find 50 tonne limit (when I have mostly 55 tonners Grrr!)
Mission 1.
1st attempt. Firestarter, Hatchetman, Vindicator, Centurion
Result: Withdrawal, Hatchetman Lost, Pilot in Hospital for 60 days, FS almost wrecked.
Mistake: staying with in range of turrets whilst trying to take down a Grasshopper, Griffin and Orion with insufficient long range Firepower leaving my spotter(s) open to long
2nd Attempt. (after having to go and find some more 50 tonners), Centurion, Blackjack, Trebuchet, Crab (heavy with LRM's, PPC , LL and AC5)
Result Withdrawal no losses, the second building destruction didn't register, despite destroying all 4 buildings.
3rd Attempt, same lance as 2nd Attempt
Result win. Managed to retreat to corner with cover out of range of turrets and sucker Opfor in 1 at a time and LRM to death. Opfor Orion, Shadowhawk, Griffin and Catapract. Destroyed turret and building the run for evac, killed 1 reinforcement too (Wolverine)
Mission 2
No drama using same lance
Mission 3
Chose heavy route. Went in with Victor, Catapult C4, Atlas II, KGC
Result win, No drama
Mission 4 (Target Acquisition). Victor, Catapult C4, Grasshopper, KGC
Result: Win but Pyrrhic Victory at best.
Mechs Lost to CT destruction, Victor, Grasshopper, Catapult (including 2 LRM15++ (+2dmg)), Character Pilot in Hospital 60 days (should be dead), Another 10,10,10,10 pilot also in hospital for 60 days (should be dead but lucky) and 3rd (10s) pilot dead.
I don't think I made any particular mistakes here, but this mission got particularly hard because the supporting lance that you get in other FP's with this mission was absent. This leaves your sole lance facing of against 12 heavy/Assault mechs + the Kurita Reinforcement lance which is 16 in total and the time limit makes it a necessity that you charge into their guns and also stand out in the open. I managed to kill 9 enemies and extract with the sole KGC and it's precious cargo of 2 Guass Rifles and ammo bins . For comparisons sake The other FP's that feature this particular map and mission but have the supporting lance (to draw fire) I usually kill all of the opfor and take minimal to no mech losses (maybe an arm here or there).
The butchers bill for me was 1 medium, 2 heavies (one quite rare), 1 Assault. 1 Elite pilot and a bunch of rare and hard to find/replace +++ weapons. Frankly it was way to high for the rewards on offer. The lostech I got was 1 Highlander 732b part and an ERPPC.
IMO this is the toughest FP out there after perhaps "the Raid" which is a player made FP.
As for taking the lighter lance in the last mission? I don't think so, there were way to many LRM's on the opfor for even full evasion lights to escape unscathed and they wouldn't have the armor to tank it out. If the mission spawns less or lighter enemies then maybe but I would need to see that was the case before trying it.