Hi
In my opinion, you should start from the gain spec. Your gain is >=70db. let say gain is 80db = 10000
Gain = Gain1* Gain2
Gain1= gm2*Rout1,2 = gm2*ro1*ro2/(ro1 + ro2) = gm2/Id2 *[ VA1*VA2/(VA1 + VA2)]
Gain2= gm6*Rout6,7 = gm6/Id6 * [VA6*VA7/(VA6 + VA7)]
VA = Leff* 1/lambda (Leff = Ldrwn - 2Ld) choose Ldrwn =1um ---> Leff = 1 - 2*0.25=0.5um
From gain equation with knowing gm2 (from GBW), Id2 (from slew rate Id2 = Id5/2) and VA ----> gm6/Id6
We also know gm6/Id6 = 2/Vov6 --->Vov6 --->(W/L)6 buy choosing Id6.
You can do sizing the remaining transistor easy. Good luck
BTW: later you will have phase margin problem because I looked at your equation , you do not mention about it