Well, in my opinion MS Project Server is great for a group of mature MS project users, but I think you will have to upgrade the standard seats to pro, if you remain with stand-alones vs. project online. The switch is very transparent, and installing the server should not be too hard since you already have sharepoint going. Portfolio management is not all that easy to setup up (at least the bit that gives you meaningful insights across groups of projects), but I’ve only tried it using the 2013 version. Perhaps they made it easier in 2016? Dunno. Good luck.