So what have you changed in your bench form that has helped? Great to see you're progressing. Personally I find using wrist straps for bench really helps and prevents me from bending my wrists too far back, but that's more at heavy weights to be fair.
How tall / heavy are you? 1500cals is not a huge amount - but if it fits your body profile then of course it's all good. I say that because I remember meeting with
@Syla5 and
@tom_e and I'm sure we put away over 1500 cals in one sitting before!
As for lower back exercise, why are you focussing on it particularly? Is there an imbalance across your body? Things like deadlifts and squats will help strengthen your lower back. However, if you want specific lower / lumbar specific exercises - try these 3:
Back extensions
Glute ham raises
KB Swings
You can try reverse hyperextensions but they're quite tricky to set up.
However I'd focus on these 3 mobility exercises, they're good endurance exercises that really trigger the core, and the supportive muscles for the lower back:
Birddog
Supermans
Planks / side planks