I know it's counterintuitive but I didn't make it up. This is from the Alfa workshop manual.You can do it that way, sure. But if you look at how the hydraulics are set up there's no reason doing one side at time would help. Won't hurt, though.
I'm telling you guys: just spend the money on the power bleeder. Buy once, cry once, use it forever. It's absolutely the best and easiest way to do the job.