I would add to the list 'keep an eye on the billing'. Once you exhaust the free tier, it could be the case that your Serverless solution is more expensive than a traditional Server solution.
I'm curious why you'd think a serverless solution would be more expensive than traditional instances once you've exceeded the free tier limits. With Lambda, you are only charged based on the number of requests and their duration. The pricing model includes 1M requests and 400,000 GB-seconds of compute time for free every month. Thereafter, its $0.20 per 1M requests. Seems very cost-effective when compared to traditional server-based solutions.