Sudden changes are indeed worse than gradual changes. There are so many different setups that saying use/don't use misters, fans, evap, a/c or whatever isn't always appropriate. Those are all ideas that may or may not work for a particular situation. A yard with many huge shade trees has...
As said, it depends on your budget. Also depends on how many eggs you plan to incubate at one time. A fan is more important than an automatic turner, although having both is best. Digital controls are awesome, but expensive.
She will likely be fine with new chicks, but you will want to watch them at first to make sure. Adding multiple birds is always easier than adding just one.