This has happened before, not crashing (just not responding for long time) when I have selected quite a few thousand parts (I was messing around with perlin noise) - not got a specific number though.
Make sure to review bug reporting guidelines to ensure what you are referring to is actually a crash.
If it is a crash, then please provide the crash dump as specified by the bug reporting guidelines. Crashes in any form are bugs that we are more than happy to immediately fix.
If this is a hang, we would more than likely just improve performance so that even selecting the entire game is performant and does not hang studio. In addition to the number of instances that @darkmodeonn asked for, if you could send a repro file to the bug group as well as your system specs (instructions in bug reporting guidelines) we can have something to benchmark against.