iPad to replace laptop as only non-phone device: Questions re: my Photos and Music libraries

To be clear...

In addition, I can keep it on an external drive in the event I ever leave Apple Music.

When using Apple Music, you never acquire "title" to any of its tracks. Once your paid subscription ends, so does your right to play Apple Music. You will of course retain ownership of iTunes purchases and your cd based music.

I will be able to store them in Photos on the iPad but not be able to back them up on an external hard drive (unless there is a way to do so I don't know about).

You can do this >>> Transfer photos and videos from your iPhone, iPad, or iPod touch - Apple Support

Once on your Mac/PC, you can move them to your external drive.

If you plan to use an iPad for more than just storing pictures and music, I would recommend forgetting a 64 GBs model and opt for either a 128 OR 256 GBs model iPad, if your budget allows.

As pointed out Apple Music is a music/rental subscription app.

So any tracks you save are not your own and the rights to those rented music tracks ends when you stop paying your monthly subscription fee.

Your only options for device backups is iCloud and other “cloud based”, offsite data storage server services, like DropBox, BOX, Amazon Cloud Drive, Google Drive and similar monthly fee data storage services.

AND/OR

There are a few special storage devices for mobile devices. There are portable, bulit-in WiFi hotspot hard drives for mobile devices made by Western Digital and Seagate.

http://www.wdc.com/en/products/products.aspx?id=1330

http://www.wdc.com/en/products/products.aspx?id=1660

http://www.seagate.com/consumer/stream/

There are special mobile lightning connected and built in WiFi Hot spot, USB flash drives made by SanDisk (now owned by Western Digital)

https://www.sandisk.com/home/mobile-device-storage/ixpand

https://www.sandisk.com/home/mobile-device-storage/connect-wireless-stick

http://www.adamelements.com/iKlips/iklips.html

This listing maybe incomplete and somewhat outdated, now. So do an online search for similar external data storage devices for iPads

Kingston Electronics makes some data storage devices for iPads/iDevices, now, too!

Good Luck!