deleting unwanted midi tracks

You need to delete the midi instruments from the Environment. if they are single midi instruments or if you want to get rid of a multi, just select them and hit the delete key on you keyboard. If you want to disable just a few midi channels of a multi instrument. select which midi channel you want to delete and turn off the Icon button in the instruments parameters box and a line will be drawn through that instrument, meaning it is shut off.

there are a few ways to create new tracks,

you have audio track 1 and you want audio track 2, select track one, then under the track menu select "create with next instrument"

or use the default key command Shift/control/return

you can also just double click on an empty track and a new track will be created, then you can change its instrument by going through the dialog menus

you can also drag an environment object to an enabled track to change its instrument

go to the midi page in the environment and delete the instrument