Question: Current hardware is a 2007 Mac mini running Lion. From what I read, I cannot upgrade to Yosemite (if incorrect, please let me know) but the question is that I also have an iPad 2 and will I be able to upgrade to iOS8 if only have Lion on the desktop/mac mini?
Per Apple's iTunes 12.0.1 support article, OS X v10.7.5 (last version of Lion) is the minimum requirement for iTunes 12, which in turn is required to sync a device that is running iOS 8.
Based on this, it can be done. Not sure if I'd want to (performance may be horrendous in iTunes on hardware that is closing in on a decade old, and that wasn't particularly powerful even in its time) but it's possible.
You're probably safe til next September/October when iOS 9 (will presumably) be released - it will probably align with iTunes 13 that would almost certainly drop Lion support.