So, I couldn't decide between the Vigilator and the Siege Breaker to lead out the Lads, so I brought them both in this list... Though I may well bring a Librarian in place of the Siege Breaker... Same point cost.
Vigilator (Artificer Armor, Refractor Field) 115
Siege Breaker 95
Legion Breacher Siege Squad (20, 3 Graviton guns and Flamer, Artificer on SGT) 400
Legion Tactical Squad (20, Artificer and Combi Melta on SGT) 310
Legion Tactical Support Squad (10, Volkite Calviers, Artificer on SGT) 230
Legion Apothecaries (3, Artificer Armor, 1 w/ Augury Scanner) 180
Legion Spartan Assault Tank (Ceremite, Dozer) 320
Mortis DN (TL AC) 135
Rapier Weapon BTTY (Quad Mortar/Thudd Gun) 60
So, basically, the Breacher Squad loads up in the Spartan and rolls forward if needed. Quad Mortar, Tac Squad and Support Squad castle up with the Vigilator leading out the Tacs for Sniper support. Siege Breaker leads out the Support Squad to give them Tank Hunter. Loads of Str 6 shooting, with Interceptor against Deep Strikers... A bit light on AA, just the Mortis really being dedicated AAA. I am also a bit concerned about the lack of real Heavy Weapons...
The other option is a Praetor leading out a few Squads of 10 in Proteus Class Land Raiders. Breachers and Praetor ride in the Spartan. Smaller numbers, but all in AV 14, loads of TL LC to shoot down something similar...