Transferring files from a Mac to an iPad

The transfer as shown in the link I posted works both ways. iPad to Mac and Mac to iPad.

Yes, you can connect an external hard drive to the iPad and transfer files that way too.

Link-> Connect external devices or servers with Files on iPad - Apple Support

You can use a hub or an adapter for that.

Short answer: Not easily.

Long answer: You can use AirDrop to transfer files one by one.

Or you can use iTunes / Finder to copy files into an app on the iPad that supports said files. Link-> Use the Finder to share files between your Mac and your iPhone, iPad, iPod touch - Apple Support

Beyond that, there's really no expectation of transferring 500GB of files onto an iPad so no real easy or direct way of accomplishing that easily or quickly.

Unless she's familiar with the iPad already it will be a major change between macOS and iPadOS and how it handles files.

There is no central Finder like there is with macOS. So all files must live inside an app. The Files App provides a file manager interface similar to Finder but not exactly the same and may not have access to files in all Apps unless said apps expose them to it.

Honestly, if she's used to a Mac, I would look into a MacBook Air. While not as compact and light as the 12" MacBook, its the closest thing to it currently.

The iPad as much as Apple touts it, is still not a Mac replacement. It can do a lot of things. But if you expect a similar experience to a Mac you will be disappointed. It will have a steep learning curve.

I can't help with Music but for Photos and documents, I would use iCloud Photos and iCloud Drive, not just for the transfer but on an ongoing basis.

I'm say "I would" in the sentence above in the loosest sense as I use both an iPad and a Mac and I could survive with the iPad but not without the Mac. Wishing her luck and hoping it works for her.

I'd seriously consider Phil's suggestion of a Macbook Air. I have one and an iPad Pro and 9th gen iPad.

The iPad Pro has a Brydge keyboard/magnetic case.

an iPad is NOT a Mac. I love the iPads for browsing, reading, and especially hooking it up to my TV to watch foreign content via their TV channel apps, but when I want to actually do something (my financials, writing letters, or whatever), I use my Macs. It drives me crazy that I cannot manipulate the file on the iPad as easily as I can on the Mac.

Aside from that, I have some problems with still semi numb fingers from my stroke (which is apparently staying at the current state it's in) and I keep accidentally hitting some area on the iPad or its on screen keyboard (because I can't feel it and don't know I am doing it) and my 3 paragraph long email or post here will disappear. So I do not care for the one finger on screen tapping like a 5 year old. It works much better with a real keyboard.

Why don't you have your wife just look at a Macbook Air at the store - take the old Macbook along to compare side by side.

FWIW, when I hit post, I realized I had magically lost a paragraph of my answer.....