Question: This seems like a typical use-case yet I can't find a way to do it-
I created a layout having multiple windows.
I want each window to open an SSH session to a **different** server.

Answer: 
1. Go to the Layout tab in the configuration dialog,
2. Select your layout
3. In the terminal in the tree view in the middle, select your first terminal, select your profile and enter at the right the "custom command"
4. Repeat step 3 for all your terminals where you want to run a special command at startup.

Use always the same layout and the same profile.

When done click on close and quit terminator.

When starting terminator again give the layout and the profile as command line option.
ie. `terminator -l Layout1 -p Profile1`

If you always want this, add an alias to `.bashrc`.
I worked with this for a while, and the ; bash advice is correct. One other piece of advice is after entering the custom commands in the Profiles area of Preferences, if you click Save, it will wipe out all of the custom commands. If you enter the custom commands and simply close the preferences window, the preferences are preserved.