Before I report what I have so far, I believe the client getting slowed down so easily is a problem.
Now, I noticed while working on a text only note that the freezing / not reponding thing has not happened. The note that was crashing EN all the time had a few dozen images inside it (and pasting a new image was sometimes the cause for EN to freeze).
The text-only note, though, still feels slower than a text-only note should feel. Selecting text is super laggy, to the point I stopped holding SHIFT to select text and I just go with the mouse, because this way EN won't lag for every character I select, but it's still too slow.
At this point I have tried:
• Restarting Windows;
• Restarting Evernote;
• Closing all other programs after a reboot and running EN only (no Chrome hogging RAM lol);
• Changing auto-Sync from 5 to 15 min (helped a bit, because it was freezing during Sync, so less Sync = less freezing);
• "Optimize Data Base" (I don't know if this is the exact name of the option, since my EN is in portuguese, but it's the first option below "About..." in the Ctrl+Help Menu);
• "Recreate Search Index for Anticipated Typing" (same as above - option is in pt, so it could be something else in englsh - also from the Ctrl+Help Menu).
None of these stopped the slowness and freezing, although EN is not crashing in the text-only note. EDIT: I went to the Databases\Attachments folder and it only had one image there. Deleted it anyway, but I don't believe it will help much. If it does, I'll report back!