I will agree with dark templar, I rarely have ever cared much about needing to rush back to base. As for the spear, normally im full deploy pylons guy, but i agree, for this mission its less needed. Still a handy way to help with my general base defense of a wall of photons around my camp to shoot down overlords trying to air drop units. Its handy if you exploit knowledge of knowing where they come from for optimal placement (trying to fully encircle the entire area is... lets just say pricey :p) Plus a few scattered inside the base because of nydus worms or whatever later on in the game. Its always handy to be able to destroy the incoming stuff before you can identify where it landed. But overall, you arent going to be able to drop more than a handful anyways in the time you have so less important. Also, go dragoons because you are going to want every bit of range you can get to shoot down the various incoming attackers. Iirc they have longer range than stalkers.