You'd be better off playing vs the CPU as practice instead of practice league.
Just did my first league game, the first of 5 ladder placement games. It was easier than any of the practise games I played. Forcing people to think faster did not seem to suit my opponent.
Underlined to me how important build order at the start is though, I had my first reaper unit into his base before he'd trained any marines at all. He wasted his time building structures but not mining enough minerals / creating enough scv's.
Was funny watching him send two battlecruisers towards me, not realising I had a fleet of 20 vikings and missle turrets sitting just outside his base. He rage quit after that.
*takes a deep breath and lights a ciggie*
Grats The last mission is epic.
How does the 4 ghost rush work then?