Complicated formula for checkboxes?

Hey guys,

I've been making spreadsheets like this to track vacations and stuff for years, but I don't use spreadsheets enough to know how to write a formulae to automate this (these are all just manual calculations by myself). This spreadsheet is for an AirBnB rental.

How can I get the green numbers in the attached screenshot to automatically calculate based on checked boxes?

In this example, each cell in column J should be $589.26 ÷ the number of checked boxes in that row's columns B-H.

Then, each cell in cols B-H, row 9 should be the sum of the values of column J only where a checked box exists.

I would love to be able to just add/remove days for people who are still undecided, thus automatically updating everyone's total dues.

Hope this makes sense!