The OOM issue is known and has just been identified and fixed; it will be part of the upcoming 5.3.0 release. You can try building from the master branch of the repository if you need to run it sooner.
“Error opening block database” usually means that your block index is corrupted (which would make sense after crashing with an OOM). If you run your node with -debug you should see an error message in the debug.log with a more precise issue. The solution here is to restart with -reindex (but you’ll want to do this with a zcashd that has the OOM fix).