I have asked her to come visit w/you...but you can also go over and visit her threads and see what she's been dealing w/and how she's been handling her teenage h living in a dorm room.
A spreadsheet of the what's coming in and what's going out says it all. Don't be surprised if he comes back later and suggests things that can be reduced and/or cut out of your life, i.e., activities for the girls, cable, etc. Some of them have done this.
I don't think you are jumping the gun to see how things will look if you have to take on the finances. I call that planning if things go south.
He can look all he wants, but he's going to discover that they are expensive, i.e., even the hole in the wall ones.
Stay calm and breathe! Try not to allow him to bait you into saying or doing something that you'll regret later. If you feel the conversation isn't going well, then end the discussion and say "we'll continue this discussion at a later time when we've had some time to think about things" and close it down. Nothing will get accomplished if you are emotionally charged and things get heated. Good luck!
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.