The node ID value ranges from 1 to 255 and is used to identify each device in the chassis cluster.
The cluster ID is also used to identify each device, but it is not part of the node ID configuration. A system reboot is not required to activate changes to the cluster, but it is recommended to ensure that all changes are applied properly.

Two statements that are correct about SRX Series device chassis clusters are:
The chassis cluster data plane is connected with revenue ports: A chassis cluster is a high-availability feature that groups two identical SRX Series devices into a cluster that acts as a single device. The cluster has two types of links: control links and fabric links. The control links are used for exchanging heartbeat messages and configuration synchronization between the nodes. The fabric links are used for forwarding data traffic between the nodes. The fabric links are connected with revenue ports, which are regular Ethernet interfaces that can also be used for normal traffic when not in cluster mode.
The chassis cluster can contain a maximum of two devices: A chassis cluster can only consist of two nodes: node 0 and node 1. The nodes must be the same model, have the same hardware configuration, run the same software version, and have the same license keys. The nodes share a common configuration and act as backup for each other in case of failure.

The application signature package is included in the IDP (Intrusion Detection and Prevention) installation directly and does not need to be downloaded separately. This suggests that while application signatures are related to and can be used in conjunction with IDP signatures for enhanced security, they are distinct entities designed for different purposes within the security framework.
https://www.juniper.net/documentation/us/en/software/junos/application-identification/topics/topic- map/security-application-identification-predefined-signatures.html

Explanation
AppQoS is a feature that enables you to identify and control access to specific applications and provides the granularity of the stateful firewall rule base to match and enforce quality of service (QoS) at the application layer. AppQoS expands the capability of Junos OS class of service (CoS) to include the following capabilities12:
Re-write DSCP values based on Layer-7 application types. DSCP values are used to convey the packet's quality of service through both the forwarding class and a loss priority.
Assign a forwarding class based on the application type. Forwarding classes are used to group packets with similar QoS requirements and map them to output queues on the egress interface.
Rate-limit traffic based on the application type. Rate limiters are used to control the transmission speed and volume for the associated queues. You can configure rate limiters and profiles to specify the bandwidth, burst size, and action for each application type.
AppQoS does not have the capability to re-write the TTL or reserve bandwidth. Re-writing the TTL is not related to QoS and could cause routing loops or packet drops. Reserving bandwidth is a function of traffic engineering, not AppQoS. References:
1: Application QoS | Junos OS | Juniper Networks
2: AppQoS for Tenant Systems | Junos OS | Juniper Networks

Explanation
The cSRX is a containerized version of the SRX Series device that runs on Linux platforms. The cSRX has the following benefits for deploying in a virtual environment:
The cSRX supports Layer 2 and Layer 3 deployments, which means it can operate as a transparent or a routed firewall. The cSRX can also support multiple routing instances and virtual routers2 The cSRX supports firewall, NAT, IPS, and UTM services, which means it can provide comprehensive security features for protecting the virtual network. The cSRX can also support application identification, user firewall, and VPN services2 The cSRX default configuration does not contain three default zones: trust, untrust, and management. The cSRX default configuration contains only one zone: junos-host. The cSRX does not have low memory requirements. The cSRX requires at least 2 GB of memory and 2 CPU cores to run2 References:
1: Juniper Security Specialist (JNCIS-SEC) (JN0-334) | Study Guide 3
2: Junos OS Security Configuration Guide | cSRX Overview 4