I rush build 5 scouts before I even think of building a Colony Ship.
My strategy is to set 100% research at the beginning so that I'll reach ion drive in two turns. During those two turns I don't bother with any new ships, because they'd become instantly obsolete. My colony ships are then designed with two ion drives, two sensors, and one life support pod.
Now in order for scouts to be useful they have to at least be able to keep up with this force speed wise... so they need two ion drives. And they have to match its range, so they need a life support module. It would be nice if they had the 1-2 sensors as well...
Problem #1: I don't think the starting game small hull can *hold* this stuff. You can't fit the twin ion engines plus the rest of the equipment so your scouts will fall behind your colony ships.
Problem #2: Your scouts with all this equipment won't be much less expensive than your colony ships. Half the price, maybe? Instead of rush buying five scouts you could rush buy two colony ships.
Don't underestimate how *many* colony ships you can build. And don't underestimate the "outward first" strategy... send your first ships out the *farthest* (unless they happen on a stupendously good planet), to beat the enemy to the planets between your civs and establish a beneficial outward border. Then fill in the gaps in between with your later ships.