First of all...glad to hear you're making your way to Texas, especially the central TX area...it's beautiful here. To answer some of your questions...
1. Assuming only that you buy inside the city limits of CP or RR, property taxes are higher in Cedar Park. The total tax rate for Round Rock is 2.293935% and Cedar Park is 2.44637%. The difference is only .01% between school districts, but the city tax rates are the big one. RR city is .36522 and CP city is .50807. Round one goes to Round Rock.
2. Noooo...the school districts are not fairly matched, even though their taxes are close. I don't know about CP, other than to say my boss hasn't been happy with that district's staff at his son's schools (that's the Leander ISD). My son, on the other hand is going into high school next year, after having been in this ISD since pre-K. You have kids...move to Round Rock...you'll be very pleased with the schools here. I moved from Austin to Round Rock in 2000, a year before my son started school, specifically for the schools! They are building a bunch of new schools, including a state of the art high school. RRISD has a unique program for its graduates too. A special note goes onto their final transcipt indicating they've been through the program. Check out their website for more info on it...
www.roundrockisd.org. Round two goes to Round Rock!
3. Utilities...not sure one town would be better than another, but I know my bills are reasonable. It just depends how cool you like your house in the summer and how warm you like to be in the winter. Just for reference, I can tolerate house temps from 73 in the winter to 78 in the summer, and my bills range from $55e & $20g in the summer to $30e & $45g in the winter. (e is electric & g is gas) My house is 1113 sq ft though, and I recently added 6" of insulation in the attic...smart move.
4. Build new vs. buy 'used' My bf just bought a new house around the corner from one that's the same floor plan and 2 years old, because of the deals the builder can offer to get you into a new house. He ended up paying less up front and overall for the house. I'd go with new if there's no price difference because you get a new home warranty from the builder with it, and they're usually right around the corner while the development is being built out. There's no clear winner between CP and RR here, but I can tell you if you want a house up to the price you listed, you can get a fantastic house in Lake Forest, Sonoma, Forest Creek or Mayfield Ranch in Round Rock. All new or newish subdivisions with beautiful homes in that price area.
5. The library...we just had a big remodeling project to the RR library in October, and someone recently retired from the library - in February. Check out the city's web for jobs...
www.roundrocktexas.gov/jobs
In my opinion, Round Rock is the clear winner, but someone in CP may feel otherwise. I presented well-researched facts...the rest is up to you and whoever else replies. I admit I'm biased because I live in Round Rock, but how else would I know all this awesome info to share it with you? I don't live in any of the neighborhoods mentioned above, and my son won't go to the new high school, but this is a great town no matter your 'station in life.' I hope you'll agree, but whatever the case, good luck with your decision and impending move! ~Kim