I want to build a Multisite Capacity Plus system, which router and/or switch should I choose?

The short answer is any professional-grade hardware you can get your hands on.

The longer answer is as long as the router is able to support the following:

• At least two RJ-45 IEEE 802.3ab 1000BASE-T ethernet ports.
• Must be able to forward at least 1 million packets per second.
• Must support Address Resolution Protocol (ARP).
• Should ideally support port mirroring (useful in case of problems).
• Must support static IPv4 routing; (ideally, also RIP and OSPF).
• Must support Network Address Translation.
• Must support Border Gateway Protocol 4.
• Must support NAT-PT if the router will be used on an IPv6 WAN.
• Must support Quality of Service (QoS) and congestion management.
• Must be secure so as to prevent DDoS and intrusion attacks.
• Should ideally firewall capabilities.

The above requirements are relatively basic and so many routers will be able to meet them. However, I would not advise using consumer-grade equipment - these may work but their long term performance and reliability cannot be assured (don't let your €x10ˣ system be let down by a €30 BPC router).

Some routers have a built-in ethernet switch which means that you don't need to have an additional switch.

There is no recommended router for Multisite Capacity Plus.

In some previous posts, I've mentioned the HPE MSR2003 and (more recently) the Juniper SRX300. These can be used on all MOTOTRBO systems but are only sold when part of a Capacity Max system.