I don't like the topology at all. the 2nd stage of ur error amplifier is not helping you at all. U need a buffer to increase the error amplifier's output pole frequency and keep the system stable enough at low loads. Since u r using an external cap (i guess) for ur compensation, u may need to increase overall gain to improve performance parameters as line and load regulation (u can do this by simply cascoding 2nd stage). Current capabilities are determined by two main things: 1st, the pass transistor aspect ratio and the operation region u want it to be (typically saturation, although there's a lot of works now with the M pass in linear region as well). 2nd, the control voltage dynamic range, in which i dont see any evident problem. Finally, use for ur transient simulations current sources instead of resistors as the load.
If this is really important to you, you should change error amplifier topology, look around !