Your account book (MoneyDance Checking 2) is quite small and probably not the problem. Possibly there are issues with a beta release of the OS software?
Does the memory footprint immediately jump to 7G or does it build up over time as you watch it.
After it "locks up", I assume you force kill the App. After doing this and before relaunching it, can you post a copy of your "errlog.txt" file?
Press the option key and use the "Go" menu in the finder to access the Library folder.
Or open a finder window, press Shift-Option-G and paste in this path