Welcome to the MongoDB Community Forums @Isaac_HP !
I believe this is covered in the Server Side Public License FAQ under “What are the implications of this new license on applications built using MongoDB and made available as a service (SaaS)?”:
The copyleft condition of Section 13 of the SSPL applies only when you are offering the functionality of MongoDB, or modified versions of MongoDB, to third parties as a service. There is no copyleft condition for other SaaS applications that use MongoDB as a database.
If your end users are interacting with your web application and you are not offering MongoDB functionality as a service, the copyleft condition of SSPL would not apply.
Server resources will depend on your application use case and workload, but 512MB of total RAM and 1 virtual CPU isn’t going to support a very large data set, especially if you are planning on running your MERS application in the same VPS.
The MongoDB Production Notes include more information on Allocating Sufficient RAM and CPU, but the best way to predict performance is using some representative test data and workload. You can always start with a small VPS and scale up as needed, but if you are planning on accessing a working set with GBs of uncompressed data with reasonable performance (or a large number of client connections) you will need to test & resource appropriately for your performance expectations.
I think a more realistic plan would be to run your application server within a small VPS or Lightsail instance and offload your database requirements to a hosted service like MongoDB Atlas which can be provisioned in the same AWS region. You could start with the Atlas free tier (512MB of data) or one of the shared starter clusters which have more storage and additional features like daily backup snapshots. Separating your application server from your database cluster will help you monitor and scale resource usage more effectively.
If your freelance project involves building separate web applications for your small business clients (i.e. you aren’t building a mutlti-tenant platform), it is also typical to factor hosting, backup, and support into your pricing model so you can provision infrastructure appropriate to your client’s budgets.