Don't overthink it. If you're going to be living on the Front Range (Denver, Boulder, Fort Collins, Colorado Springs), you're not going to be all that high (5,000-5,500 feet in Denver and anywhere north of Denver, 6,000 feet in the Springs). This will make your workout paces a little slower (about 10 seconds per mile) and will require a bit more recovery, both in terms of time between intervals (take 90 seconds instead of 60, for example) and days of rest after races or hard workouts. Do your workouts and incorporate strides 2-3 times per week and you won't be sluggish at all.
As far as "live high, train low" goes, that doesn't really exist in Colorado. You can live REALLY high (8000-10,000 ft) and train moderately low (5000 ft), but there's nothing below 4000 feet that is easily accessible without flying or driving for 8 hours. Think of it as an opportunity to get really strong. Run lots of hills and challenge yourself knowing that every run has the added difficulty of thinner air. The altitude will make you tough even if you are a total non-responder to altitude from a scientific perspective, and most people won't gain all that much from 5000 feet. The real benefits come from the increased difficulty of everyday runs, the abundance of soft surfaces, and the slower paces you'll have to run on your easy days and long runs, which will make you fitter and help you avoid injury.
Also, remember that many champions have been made in CO and specifically the Front Range: the Gouchers, Emma Coburn, Jenny Simpson, Ritz, the CU Buffs. Enjoy your time here!