yeah, sometimes reaper will not immediately recognize new waves plugins. usually a whole rescan solves it. which is a pita.
concerning crashes i have found that vst3 versions crash a lot less, so i use them now as default.
i always check which plugins are prone to crash by duplicating tracks with those fx on it. i find that if reaper stays up an running then, there's a lot less chnace of anything bad happening down the line.
this is in no way scientific, just anecdotal