I must not have hit the reply button.
I'm less worried about the achievement points. Assuming the guy leveling you is fine with doing this.
Go kill some bosses first. Skeleton King, Kulle, Maghda, Belial, and Azmodan. All really easy to get to, and the leveler will clear them out in ~3 seconds, giving you about a half dozen achievements for each.
Kill, Kill fast on Torment, ~3 challenges, and the coop achievement. I just listed 5 bosses, so ~30 achievements total. Getting to 70 is worth at least 100 points. So, with help, you can probably get all the points and leveled to 70 in under an hour. Throw in bounties that are events with achievements for completion and coop completion, 400 achievement points are nothing.