Consequences of upgrading Mac Pro 10.6.8 ?

Hi all, I have a 2010 Mac Pro (yes 12 years old and still brilliant!) 2x 2.4 quad-Core Intel Xeon which is perfect for all my design needs and runs wonderfully apart from browsers being out of date and any new utilities not being able to install.

I have avoided upgrading the OS 10.6.8 for many years for fear of my existing applications no longer being compatible. I use InDesign / Photoshop / Illustrator etc. (CS 5.1) which are all original applications that I bought and still have the install DVD's - they all do as much as I need and it has meant that I haven't had to subscribe to Adobe to use these applications.

Can anyone advise me as to the pitfalls of me upgrading my OS to above 10.6.8? I am worried that none of my existing applications will be compatible and that I will be forced into subscribing for them.

I don't want to sound like a meanie miser, but why pay for something again if it does everything I need!

Any advise or experience anyone has that they can share with me will be very gratefully received.

Matt