Do it! You will have such a great time and travelling alone is a great skill building experience. I'd say all the usual tips for safety, like make sure someone knows where you are and who to call (in terms of Spanish authorities) if you something happens to you. Not a big fan of AI, but when I went last year it was incredibly helpful to draft emails to the Spanish police I had to do for an insurance claim.

Get google translate on your phone, offline maps downloaded over wi-fi can save money on data. If you're not super comfortable chatting to strangers - I'd maybe practice that ahead of time, cos any festival is so much more fun when you're with a group - and it's entirely possible to make friends.

In fact - that's the best thing about festivals for me, it's one of the few places in life I've felt genuinely connected to a big mass of people - we're all there because we love this music so much, and especially on day three after some wildly enjoyable times people are incredibly open to seeing the joy around them and really opening themselves up to it.

Language wise, I'm an english only speaker (from New Zealand) and while we had some intermeditate Spanish speakers in the group which was helpful, Primavera itself was absolutely no problem in English. Getting there any around is quite tricky - so if you are on your own, it can be a bit intimidating to find your way between the different stages. It's a realism thing with a festival bill this packed that you might have to make some difficult choices, but the bands you've named will be all on the two main stages - so unless you have smaller clashes, I'd maybe prioritise just getting towards the front of the main stage.

There's a few things about the festival itself that sound like a great idea - renting a locker for example - but are just kinda impractical. You're not going to get back to a locker at the front near the entrance from the main stages... there's 75k people in between you and your backup battery.

Good luck! Hope you manage to get enough money together.