As far as I know there is no catch with the Aggie Network Gmail. It would be a great place for those pictures etc.
The Raspberry Pi is a small computer that is a little bigger than a deck of cards. It is probably the cheapest option, but will be a little more cumbersome to set up. Some of my co workers use Kodi on their Raspberry Pi's and access all of their media that way. They hook them up (via 4k HDMI) right to their home recovers.
https://mediaexperience.com/raspberry-pi-xbmc-with-raspbmc/You can now load your OS on an SSD with as raspberry pi. It uses a USB 3 port versus an sd card. That could be an upgrade to what's posted above. Argon 40 makes an SSD case with full size HDMI ports.
Again this is a bit more cumbersome and you may want a tech savvy person to help you out.
The cons of a NAS are really price and speed. They can get expensive fully loaded with hard drives. They are fast enough to watch movies and do most basic things. But they are not fast enough to really work on large complex files or edit video directly from them. They have NAS drives with 10 Gbe ports. They are just pricey. A thunderbolt hard drive array is much faster and cheaper per TB versus a 10 Gbe NAS but it is on a leash versus having network connectivity.
Personally I would use something dedicated to stream media. If a raspberry pi is too complicated and a NAS is too expensive, a mini PC (even used) my just be what you are looking for. Especially combined with a 'desktop external hard drive' for your storage.
Another poster in this forum talked about mini PC's and I bought an intel NUC to interface with a projector and some AV equipment. It is awesome. The nit below has Win 10, and USB 3.1, fast enough to connect an external dive full of movies.
https://www.newegg.com/intel-nuc-dn2820fykh/p/1VK-004K-008J5?Description=refurbished%20intel%20nuc&cm_re=refurbished_intel%20nuc-_-9SIAA0SAKE1675-_-Product&quicklink=true