I have a python bot which I'm hosting on digital ocean. 
Right now to run it persistently I'm using virtual terminal screen and I see that this way is far from stable. 
How I can schedule my bot script to run forever and being re-run if it crashes ? 
And also how I can schedule some other python scripts to run once in an hour ?
You can use crontab to schedule process.
To run hourly, you can use like this

0 * * * * /my/program/path

(minute, hour, day of month, month, day of week)
Run Python script persistently on server