Hi ihearanewworld, welcome on this board, and sorry for the delay of my answer.
Yes Indeed , there are resizing issues in Reaper. I suggest to go in reaper preferences, plugins section , tick "automatic resize fx windows" UP AND DOWN and Autofloat newly created fx windows.
About the sizes, i.e on a macbook 15.6 inch screen . perfect size is at 60% to fully enjoy the upper toolbar, browser...
About state recalling, we are aware there is some issues with VST3 versions in reaper, we are still investigating on this one, seems it doesn't happen on every synths. We often suggest as a temporary workaround to work with vst2 versions.
It would be great if you could please post some informations here :
your version of OSX
reaper ( last one is 5.22)
what soft and versions which have wrong state recall ( VSTI / VST3I / AU )
hope it helps a bit,
Best