The main strength of an immo deck is its awesome speed; one immo allows you to dish out a powerful hitter turn 1. So you want to be able to play you hitters with one immo. Lava golem is ideal for this unupped. Phoenix is also manageable, but slower unless you have upped immo or fire towers. Crimsons can't be played fast enough, so better to use golems.
As for support, one or two novae is nice for deck speed. aside from that, you want a couple of bow hitters (Lucan, forest spirit) and control (deflag, lighting/reverse time, nightmare, etc.) Thunderstorm and purify are also nice one-offs. Finally, reduce deck size to 30. Anymore will seriously delay the immo combo.