Capacity planning / Scheduler ( 2 questions )

I have these 2 general questions. I am starting to research these.

  1. We have some JVM applications and need to figure out how much RAM and cores and storage we have to recommend to set up our clusters. Are there capacity planning guidelines( or formulas ) we can use ? I understand that capacity planning is a big topic but I wish to start with some basic resources like RAM etc.
    I have to point out that we have istio pods too. So I believe this could get more complex. Right ?

  2. Is the scheduler in Kubernetes extensible ? Can I consider it for scheduling and integration with a Spring application ? So on AWS it would be an external orchestrating scheduler like CloudWatch. We want to fire based on schedules stored in Oracle and we would like to invoke Java code. Am I looking at the wrong tool set for this ?