#8 Drizzt,
It does take some time to develop the population with only 1 colonist, but planets at this PQ level are money-sinks until the basic infrastructure is built. Also, too high a population on these planets acts as a "speed-brake" on your overall development, since it is these system's morale which plummets once taxes exceed 20-25%. (Sol and other PQ20+ planets can easily take tax rates of 50%+ while maintaining an acceptable morale.) In the early game, you are better served putting your efforts into better quality planets.
The goal here is to (a) define borders and (b) maximize ROI (return on investment).
By the time the basic infrastructure is built (Soil Enhancement/Bank/Research Lab/Fusion PP/Mfg Center), the population will have grown to 75-100 and will start to fully utilize the improvements.
Larger populations do produce more IU's, but (generally) this results only in a 1-2 turn improvement in completion rate. If you need to rush something, you can make this time up by purchasing and/or leasing it. You will usually have more cash available to do so, since Earth has not been so depleted (settling 100+ colonists on every planet), and thus a greater number of taxpayers have been contributing to revenues (and at a better rate).
The only detriment to this approach is conquest. Aside from Earth, most planets will not be able to field TR's/Combat TR's until mid-game. But if you have a Sol-equivalent PQ system alongside the PQ15-17's, it will keep pace with Earth and allow 2-3 TR's to be fully embarked.
#8 Zorven,
Build a Scout as your first ship. Send it in the opposite direction from the Hero. Build a 2nd one on your first colony. With 2 Scouts and the Hero, you can uncover most every system nearby before colonizing.
This is actually a timesaver - you don't want population embarked on colony ships and unable to grow or produce taxes. Leave them on Earth until you need them (produce the colony ship, but don't launch it).
Population size does affect production, but not enough to worry about on sub-PQ18 worlds. There are no published figures on production, but usually only PQ18+ worlds will benefit from populations greater than 100 at start.
~SDC~