I'm afraid there isn't a direct way to accomplish all of the needs.
You can set a deadline on the Variable task.
You can set a Start No Later Than constraint on the variable task.

You can make the variable task a successor of the Jan tasks however a F to S relationship is always the later of the two. So if the first task moves to past Feb 1, you'll need to manually remove the link to the Jan task and re-link to the Feb 1 task.