Access 2010 to 2016 upgrade questions

AccessDev I can't think of any security related issues you're likely to encounter, but that's something only you can determine by examining each accdb for any security features implemented. It's sort of hard to predict since we don't really know what, if anything was implemented. Inherently, though, there should be no lessening of security. But then, Access is not known to be a highly secure application to begin with.

You are likely to find at least a few differences that may require updates, but again, each accdb is unique and will need to be checked.

I can state that more recent versions of Access have been less tolerant of ambiguity in VBA, so you may find yourself revisiting some of the code to provide fully qualified references. 

And, of course,  if any of those accdbs implemented features deprecated in later versions, they'll need to be addressed. 

On the whole, it should go pretty well, though.