If I follow this guide, won't the resulting p2pool node be largely unknown, and effectively private?
If you want your p2pool node to be reachable by other nodes and/or miners, you must allow inbound network connections on ports 9333 for other nodes, and 9332 for miners.
I'm a little unclear about merge mining. It sounds like if merge mining is configured, that the resulting merge mining proceeds goes to the pool operator. Is that the case?
At the risk of sounding selfish, if I carve out processor resources, set up a public node, and pay for the bandwidth and power and collect no fees, I want to see if merge mining can help justify the operating costs.
If the port(s) above are open, most scanners will recognize your node automatically and list it on their sites. Some you may need to request your IP be listed. Merge mining is, essentially, solo mining and all block awards go directly to the node operator's coind core client wallet used when starting and running p2pool with the merge mining parameters.