SRE Agent support multiple subscriptions

One of my Customer building 3 PoCs and they have few technical requirement that are unclear from the documents. It would be super helpful to get technical guidance and documentation supporting those requirements.

1. Does one agent can access resources across all subscriptions connected to a Lighthouse tenant. Their current infrastructure setup, where a single Lighthouse tenant is used to manage multiple underlying tenants and their subscriptions. In this scenario if an SRE agent in one subscription could access resources across all these subscriptions. Is there an upper limit?
2. Is there a upper limit for number of resource group an SRE agent can manage per subscription? 
3. Are there cost optimization best practices for scenarios like pre-recorded scripts or agent-level improvements for repetitive tasks in their case VM resizing?
4. From billing standpoint does always-on agent connections incur charges even when no alerts are active?
5. When handling multiple remediation tasks or queries, does the agent execute them sequentially or in parallel? Additionally, is there any control or configuration available for managing concurrency?