CMS Made Simple Forums

I have a lot of CMSMS websites on my server and want to upgrade the php version to 5.4.3 or higher.

There are some website with an older version CMSMS. Do I get some problem wich the older version?

Wich version of cmsms has it to be it at last?

You can never get an answer to that. It depends on so many things, not only core but also third party plugins. Trail and error or the best option: upgrade them all!!!