BASH: send SIGTSTP signal (ctrl+z)

Do you want to just start it in the background? For example:

mycommand &

If you want finer grained job control, you can emulate Ctrl-Z and bg. Control-Z sends SIGTSTP ("tty stop") to the program, which suspends it:

kill -TSTP [processid]

And the bg command just sends it a SIGCONT:

kill -CONT [processid]

You don't. You put an ampersand after the command.

command1 &
command2 &
command3 &