If you plan to keep using your new iMac for the next 5 to 7 years, which is NOT unusual, you will not want to be stuck with and OS that is at least 8 years old!
Yosemite has been around for at least a year and El Capitan is almost ready for release. Given your apparent anxiety and reluctance to upgrade, why not wait for a little while after El Capitan is released and install it after the first update to it?

I'll presume that you will continue to update the Adobe Apps as the years go by and perhaps one of those updates will REQUIRE El Capitan or later, leaving you with another choice.

Bottom line, wait for the first version upgrade to OS X 10.11 and then install. Meanwhile, ALWAYS install ALL the updates that Apple throws down at you. They are specific to your machine and the software that you are running.


P