Ask HN: Questions about mobile app architecture

Hello HN, I am currently developing a mobile app with Cordova and ionic. The overview of the app is its meant to help people schedule events with friends. I do not have much experience working on the backend of apps so I am looking to see what the best options are. I completed a online class that gave me a 1000$ AWS credit so I have been exploring their solutions. If their is something dramatically easier like Parse or Heroku for my use case let me know, the new hobby tier DB and Dyno are within my budget. It seems like the three best options I have are to 1. Run an EC2 instance with a Node.js server and Mongodb database to handle all of the business logic and ajax calls from the app to update the DB, the issue with this solution is I am worried about the amount time devoted to system admin would be huge. 2. Run a Node.js applications within Elastic Beanstalk container and use the DynamoDB database 3. Use the Lambda service to get away from all of the server admin along with DynamoDB. Option number three would seems like it would be the quickest and easiest to get up and running but I am very scared of waking up one morning realizing that a bad infinite loop has cost me thousands of dollars(Is it possible to shut everything down if it goes past a price milestone?). The 2 services I am nearly certain I am going to use are the Simple Notification service and the Cognito service for easy user logins as well as S3 for content storage. The amazon credit only lasts a year so I am fine with using around 70-80$ a month on services. I also think its pretty safe to say I will have less than 10K users so it seems like the load is not going to be huge. Let me know if it seems like its a fundamental flaw to use node, how I understand it is I will write an API that the apps use to handle business logic like updating the database and scheduling notifications.

Sorry for the poorly structured post, I tried to fit in all the relevant info. I will clarify anything in the comments.