The guide that @CptnCrnch provided should give you all the sizing information you need.
For logging you will get some events logged into the event log for the network, Network-wide -> Event log, and right at the top (next to the Event Log title) you can use the drop-down to select events for security appliances. This will give you a certain level of detail, such as content filtering blocks, IPS updates and events.
If you want more detail then you’ll need to set up a syslog server and configure the network to use that, Network-wide -> General then scroll down to reporting. When you configure the syslog server you can select what to send to it. I believe selecting Flows (but could be URLs, or Security Events) will provide a bit more detail as to which firewall rules are being hit in the Syslog messages, but you’ll also need to turn on logging on the firewall rules too - which only becomes an option once you’ve configured the Syslog server for the network.