I login by SSH and tunnel port 80 of the server to my remote pc.
Not sure I follow you on that. I don't see a need to tunnel anywhere if your traffic is all LAN. ( or even if it is not). SSH server allows direct connections on port 22. Lets assume you use windows clients to access a "Nix server via ssh over your LAN only. Putty, WinSCP and even xming ( if you need x-window forwarding for any reason ), are excellent tools depending on your needs. No tunneling required. Place exceptions in your servers firewall configuration for just the clients you will be using to connect via ssh, edit ssh config to deny remote root logon, and have at it. I access my wordpress server via ssh on my LAN every day using all the tools mentioned above, connecting with just the internal IP address. I access wordpress, phpMyAdmin, and my web apps with a browser using http and https. I'm not sure why you would want to tunnel to reach applications that run on ports 80/443 (phpMyAdmin, TikiWiki, wordpress). I think SSH is for secure shell access or secure file transfer. Are you confusing SSH with SSL?
Is there a way to access WP by LAN-IP as well as localhost?
To access from the LAN, your wordpress urls must contain the internal network address of the server. (ie.. http://10.x.x.x/wordpress). If you still must access wordpress from the localhost ( the server it's installed on ) placing an entry in the hosts file that resolves it (127.0.0.1) to 10.x.x.x. should allow you to do that as well.