Ubuntu After Install https://www.thefanclub.co.za/how-to/ubuntu-after-install
Program allows you to choose the applications from a list you want and will install them all at once along with the PPAs.
> I'm thinking I'll dual boot the system
Not a bad idea. I did the same thing for the laptops I configured for my mother and my uncle. At first they were hesitant to try Linux, because of course something that is free cannot possibly be good... But they eventually started booting up Linux more and more as it is running faster and has all the tools they need. One big hurdle for my mother was the lack of Office 2013, but the combination of Google Docs and WPS Office is keeping her (begrudgingly) satisfied.
> What would be a good starting OS?
What are the specs? If it's something older, go for the MATE or XFCE desktop. I maintain Ubuntu MATE 16.04, Linux 18 MATE and ChaletOS 16.04 (XFCE) on various older machines (recently upgraded from their older counterparts) and they all work fine. If it's something powerful enough to handle Cinnamon, check out Linux Mint 18 Cinnamon. It's running on the machine I type this post on - my old PC from 2009 currently donated to my family as a media center (AMD Athlon II X2 245 / HD4650 / 3GB RAM).
If you have enough time/feel like it, you might configure the installations so they are a bit more easy on the eyes / Windows-alike. I love mint for how well it plays with most of the PCs/laptops I threw it at, but the icons & fonts are a bit tiny/blurry on some displays and the default back menu was ineligible for my shortsighted uncle.
You might want to check out: https://www.thefanclub.co.za/how-to/ubuntu-after-install It's a script that helps to quickly install some more commonly used software. Makes installing stuff on many machines easier, and it's simple enough that even new Linux users can use it to add some new extras they need.