Using an external storage device to store offline playlist

[BarbaricWafflez]

So I have somewhat of a unique problem I'm trying to solve.

I have a Spotify playlist that I'd like to make available offline so that I can play it in my car while I'm driving.  Currently, the playlist has 2,648 songs and is 197hr 27min long, but it's my main playlist, so it's going to expand as I listen to new music, which I do often.  I've previously been using my first generation Kindle Fire, which I connect to my car with an aux cable, but my Kindle only has 8GB of storage (officially it has 8GB, in reality, once you account for the fact that they rounded up and once you take out sufficient space for the OS and the added junk that comes on the Kindle which can't be uninstalled, you really get <5.5GB of storage space), so if you haven't already guessed, there isn't enough room for my whole playlist on my Kindle.

Solutions I've thought of:

1) Buy a new tablet with more disk space -- Probably the most obvious solution, but there are a few drawbacks.  One, this would be the most expensive solution, and two, as far as I can tell, there are no tablets that come with anything more than 64GB of storage space.  Now, I read on a forum thread here a way to calculate your playlist size using your playlist length (in minutes) and your download speed, and based on those calculations my playlist is going to be a little less than 30GB.  And like I said, I want there to be plenty of room for expansion, and a 64GB tablet would probably give me enough room to reach about 5000 songs on a playlist.  That's good, but I'd like to do better if I can.

2) Buy an external storage device for my current tablet -- This sounds like it would be cheaper, but this is the tricky bit.  Suppose I had an external storage device for my Kindle.  Could Spotify access that space and download excess music there?  And even if I could get it to do that, would it be able to play those songs both on the Kindle and from the external storage device?  I'm not much of a techy, but this sort of setup sounds shaky to me.

Thoughts?  I really appreciate you taking your time to read this, and I welcome any ideas/suggestions you might have. 😃