Are the pots currently planted with anything? Is there a working drip or overhead irrigation system? Do you have any other equipment, for example, a bobcat, small digger, etc? Is there a fertilizer injector? How big are the colorado spruce? Are they pot in pot or field-grown? If field-grown, what are the soil characteristics? (clay or sand) Do you know how to dig a tree?
What type of market can you serve? Are you ready for the hassle of retail? Wholesale? Both? It's a huge commitment of time and money.
Ask lots of questions. Contact the local extension agent. Check with local landscapers -(real ones, not guys with a pickup and an opinion)- and ask what sells best in your area. What do they need? Join the state nursery association. Check University websites. Get your name out and lots of people will help you, as long as you are honest and are not perceived as a future competitor.
Develop a relationship with a liner grower. Determine your turnover time. If you want to sell 2'' diameter trees and want to do it in 3 years, you'll have to start with 1 1/4-1 1/2 whips. They are pricey. If you have 7 years for a crop to grow, then you can start with liners that cost only a few dollars each. Find suppliers in Nursery Manager Magazine on-line.
Grow varieties that are not currently under attack by an invasive insect or fungus in some other part of the country. No ash trees, walnuts, red oaks, etc. or the pest WILL get to you, about the time you have a nice crop and the genus goes under quarantine.
Consider a niche market: fruit trees; trees "experts" call natives; or conifers only, for example.
Research your market. Research your crop. Start small, hold your breath and hang on! Good luck.