MEAN.JS setInterval process for event loop (gets data from another server)

I have a mean.js server running that will allow a user to check their profile. I want to have a setInterval like process running every second, which based on a condition, retrieve data from another server and update the mongoDB (simple-polling / long-polling). This updates the values that the user sees as well.

Q : Is this event loop allowed on nodejs, if so, where does the logic go that would start the interval when the server starts? or can events only be caused by actions (eg, the user clicking their profile to view the data).

Q: What are the implications of having both ends reading and writing to the same DB? Will the collisions just overwrite each other or fault. Is there info on how much read/write would overload it?