Is it intended for old players? Or is it made to simplify the life of newcomers? Assuming it is the second; what are the buttons these people pay attention too? Play. They want to play the game with minimal effort. Sometimes, a friend of said person has a server hosted, so he or she will need to refresh the server list. It might have a particular name so they will use the filter box, to search by server name. But wait! Odamex is more than a simple multiplayer port: it attempts to keep as close to vanilla as possible and allows single-player games, so why not prompt a dialog box with the Doom games available in his/her PC, once the player hits the single-player button (maybe with some pwad management)?
That being said, why not leave these three buttons (play single player, Join server and Refresh list) and MAYBE the search box in the tool bar, and hide the rest under "show advanced buttons"? Adding text to said buttons could be interesting, since the icons doesn't tell much (an orange O and a red O ...?). Make these large and, maybe, scalable to the window size.