Cubase 9 is fine with VST2.x plugins, but be careful as old VST2 might not work correctly.
You cannot use 32-bit plugins in Cubase 9 - bit bridge is now gone (and good riddance) but J-Bridge may still work.
To check 32 or 64-bit, look at where it is installed. If the dll is in the “Program Files (x86)” folder it is 32-bit.
There are several possible install locations, which does not help:
C:\Program Files (x86)\VSTplugins
C:\Program Files (x86)\Steinberg\VSTplugins
C:\Program Files (x86)\Steinberg\Cubase_x\VSTplugins
C:\Program Files (x86)\Common Files\VST2
C:\Program Files (x86)\Common Files\Steinberg\VST2