upgrading and organizing new mac mini upgrade from mac pro

OK, so I bought one of the new mac minis to upgrade from my beloved 2008 mac pro.

I was wondering if anyone had any good strategies for organizing with the small internal ssd drive. I upgraded to the 256 internal drive but that is a far reach from the terrabytes of internal storage I have on the mac pro's 4 drives.

I plan to put an external thunderbolt drive into the mix for obvious things like photos and my itunes library etc.. but how else can I minimize what I keep on the main internal drive?

For instance, my iphone and ipad backups... is there a way to point itunes to an external place to keep them even though the default is in the library?

I havent migrated to a new computer in 10 years and I know thing have changed quite a bit so the task is a bit daunting.

thanks!