Q.Zones
I live in Zone 8b. If plants/trees suggest they grow best in Zone 2 to 7, would that be a bad choice for Zone 8?

A range of 2-7 implies that a zone warmer than 7 may be too warm in winter for the plant to thrive. The second number, as in 2-7, indicates that the plant needs cold-induced dormancy to trigger spring growth and blooms. So, if grown in zone 8, it may not flower. To double check, search the internet for the plant's heat zone. Confusing!
http://ahsgardening.org/gardening-resources/gardening-maps/heat-zone-map
https://www.gardeningknowhow.com/...zone/zone.../zone-8-sun-tolerant- plants.htm