What is the ideal scope of a Component? What does it include and how many rulesets should it be comprised of?
Consider a Component like an independent application layer. It has as much or as little in it to deliver a standalone capability, so there is no such thing as a Component that is "too big" or "too small".
Review some of the Components available from Pega Marketplace as reference points, for example:
The Sharepoint Online component for web content storage has numerous Connect-REST rules (for each of the key Sharepoint API operations an application may choose to use), Data Pages that wrap the Connectors, associated Request/Response Data Transforms, and an Authentication Profile for authenticating to Sharepoint Online.