How to launch a set of program inside tmux or gnome-terminal within a script?

Open a tmux session and start the first command. Then launch more commands on new windows and evenly distribute the window sizes at the end.

tmux \
  new-session  "command1 ; read" \; \
  split-window "command2 ; read" \; \
  split-window "command3 ; read" \; \
  split-window "command4 ; read" \; \
  select-layout even-vertical

The read after each command causes the window to stay open after the command has finished so that you can read the output.

tmux new -d -s my-session 'echo window-1 pane-1; sleep 8' \; \
          split-window -d 'echo window-1 pane-2; sleep 6' \; down-pane \; \
            new-window -d 'echo window-2;        sleep 4' \; next-window \; \
                attach \;

The above is a running example of the general idea ... more here: How to run streamripper and mplayer in a split-screen X terminal, via a single script

If it's always the same configuration of programs, you can use a tool like teamocil.

You'll need to create with a configuration (e.g. ~/.teamocil/sample), which contains something like:

windows:
  - name: my-first-window
    root: ~/Projects/foo-www
    filters:
      before: "rvm use 1.9.2"
      after: "echo 'I am done initializing this split.'"
    splits:
      - cmd: "git status"
      - cmd: "bundle exec rails server --port 4000"
        width: 50
      - cmd:
          - sudo service memcached start
          - sudo service mongodb start
        height: 50

And then you can run: tmux new-session -d "teamocil sample" \; attach