So I recently made myself a new workout, this time a 4 day routine. It's been going great on everyday, except my shoulder day. It's really bothering me. I've been on this for 3 weeks, so today was my third shoulder day. Here's what I did, then I'll explain my problems:

Shoulders
Arnold Press: 3X8
Dumb lateral raise: 2X8
Bent over rear delt row: 3X8
Bent over lateral rear delt raise: 2x8

Traps
Dumbell shrugs 3X8

Abbs
Decline sit ups 3X8
Hanging knee raises 3X8
90-degree crunches 2x8

Okay, so with how i wrote my workout plan, I can also do a few different excercises. For example, I sometimes do barbell shrugs (another 2 or 3 sets) and sometimes barbell upright rows.

Anyway, my problem lies here: I'm struggling to hit all 3 shoulder blades in a reasonable set range. I thought I was doing really well with my bent over rear delt raise when I glanced at the mirror and saw my back was arching so bad I could have rolled down a hill. So, I dropped that. I then thought of doing cable face pulls, but the weight brings me in forward so it's hard to maintain form. Also, when doing bent over lateral rear delt raises are you supposed to hunch your back like that? Is that okay? Also, I'm struggling to really hit my obliques. Are heavy side bends okay? And if I do those (2 or 3 sets) then I'm up at 11 sets. Is that okay? I tried russian twists today on a decline bench but my abbs were so spent I couldn't hold myself at an angle to do russian twists. And, after my shoulder workout, my traps felt pretty hit anyway. I think the bent over rear delt raise's really killed my traps so I moved on without doing the barbell set. Anyway, how can I hit all 3 shoulder plates in a reasonable set range.

Suggestions are needed badly, thanks.