EDIT: Missed the Commisar Lord hiding at the top
I'd look into picking up a Leman Russ or two as your next purchases (Demolishers or Exeuctioners ideally, normal
LRBTs with Plasma Cannon sponsons are brutal as well). I'd also pickup a
CCS with 4x Melta or 4x Plasma and put it in a Chimera. Honestly, I would drop the Chimeras from the Infantry squads an run them as a blob squad with the Commisar Lord attached to it (once you pick up
th CCS you can downgrade him to a normal Commisar and he'll fill the same role for less points). Give the Chimeras to the vet squads, and then if you want you can still put them in the valks and just leave the Chimeras empty on the table. I'd also consider switching the Valks for Vendettas, especially with the alck of real
AT firepower in the army right now.
You're off to a great start though!