To know how many CPUs and how much RAM and disk Disk space to use, the most important factor is how many requests you will be tracking per month in Matomo. Other factors which would impact server capacity planning include how many websites are created, and how many user segments need to be processed.
As a general rule, when tracking more than 1 million user actions per month, we recommend to have at least two servers, one for the database and one for handling all the HTTPS requests (Tracking, API) and the Report processing.
Below you will find general recommendations for which instance types to use. While these should work well for most cases, you may need to adjust the instances types to suit your processing workload.
You can find some recommendations here, if your use case is different please get in touch with us.