Sorry I can't help you with the freezing-problem, but that one can't use V4 add-ons in V5 is plainly not true. Moving installed add-ons from V4 to V5 is as simple as copying the add-on.xml to V5's add-on folder. Some (not all) airport add-ons might need a custom exclusion to "get rid" of the updated airport buildings LM gave us in V5, but I've installed literally hundreds of V4 add-ons into V5, and off the top of my head I've had to draw a custom exclusion for one out of seven of those airports to make them fully compatible - a matter of minutes. For payware, there are often pre-compiled exclusion files available.