My full node has been completely synced for a while, but it never shows anything different that "8+0 connections". What do those numbers mean? Shouldn't they increase over time?
8 is the number of peers that you are connected to. 0 is the number of peers that are connected to you. if you want to allow others to connect to you, you need to open port 18080 on your firewall/router.
You can set the number of your daemon outgoing peers (ie, peers it connects to) with the command line parameter
--out-peers. The default is 8.
For having incoming peers, you need to open up your firewall for your daemon's p2p port. This port is typically 18080 but can be customized with the
--p2p-bind-port. I think you cannot limit the number of incoming connections.