Any privacy considerations regarding allowing inbound connections for a Tor full node? I wanted to know if there's any privacy considerations to take into account when opening the bitcoin ports on the router for a bitcoin node.

I'm using -onlynet=onion in the bitcoin.conf file and I did not modify any tor config file.

I also wonder if a remote port scan can detect I have a bitcoin port open in the router and whether changing to a random port would help privacy. thanks.
If you are running -onlynet=onion, there is no need to open any router ports. Perhaps I misunderstand your question. 

If your chain state is caught up, and bitcoind+Tor is properly configured, you should be serving data to other nodes, even behind an otherwise locked-down home router. 

What result do you get when running 

$ bitcoin-cli getpeerinfo | grep true