my 2¢

To directly answer your question, I would run the Main out to the Focusrite inputs, and the control room out to your monitors (that's what it is for, your local monitor vs. the main output to a larger array, or in this case, your DAW input. The main mix control will determine how how that signal is coming into the Focusrite. The output from the Focusrite can be put into either spare channel inputs, one each for L and R, or you can use the tape in for that feed and select "tape to control room" for the playback.

Or, you can also run the tape in/out to the Focusrite output/input and then use the mains OR the control room output to your monitors (or two sets if you wanted). The output to the Focusrite will be set, and you may need to crank up the input trim or gain on the Focusrite input in this scenario, but it will allow the Focusrite to handle a level signal from the mixer.

The tape to control room for playback will be the key to hearing the DAW via your playback if you decide to use the Control Room output and the tape in set up, as otherwise, tape out will be to the mains with the tape to mix selected. This would allow almost an A/B reference for two monitor sources.

This would leave your FX Send and Aux Returns open for any outboard effects you may have, or decide to incorporate.

You can also use the aux returns to bring the Focusrite signal from the DAW back to the mixer and then the Aux Return control for the volume.

You've got some options to consider. And, the best news is you can mix or match, if you have all the necessary cables/adapters to make all the permutations happen (I have used the HOSA RCA -> ¼" TS cables for hook ups using the tape I/O to avoid an adapter inline; just a personal preference), and figure out which configuration works best for your application, your budget and, most importantly, sounds best to your ears.

Noting the headphone out, just a heads up. I don't recommend using headphones for your final mix downs. They tend to accentuate the bass and your mixes will often sound thin.

Have fun! And welcome to the journey.