Go to your local convenience store, or Walmart, or whatever. Buy a pay-as-you-go smarthpone. Might cost you as much as $50. Buy a pay-as-you-go (PAYG) plan to go with it. Maybe $50/month.
Create a Gmail account with that phone. Use that Gmail account with that phone. If you're really super-paranoid, avoid places that have surveillance cameras (if possible) or if you have a buddy who runs a 7-11 and you know he erases the tapes every week buy the PAYG cards from his place. Always pay cash for all of the above.
VPNs can be tracked. It's just usually not worthwhile for the cops to do so. They can track you this way, too, but it'll take them more time.
If all you're doing is hobbying, this is probably already 3 levels of paranoid too far. That's a good thing. If you're engaging in drug trafficking, gun running, identity theft, human trafficking, or terrorism, your offenses will be big enough for the cops to put in the effort, but for regular non-pedophile hobbying? They don't have the time for that. The time they spend catching you, they'll be letting a dozen, less careful guys get past them.
For a hobbyist, be the biggest pain in the ass for them to catch. If all you're doing is seeing an MPA or an SP, you're not worth the warrant to track the GPS signal on your PAYG phone.
There is no such things as true anonymity these days. But you can make it too difficult for a casual attempt to figure out who you are, and that needs to be good enough.
Oh: and I've seen the Gmail screen asking for your phone numbers. LOOK FOR THE SKIP BUTTON. I'm pretty sure you can skip that login requirement. They're asking for your phone as a backup if you lose your password or if your password is hacked. If you're too cheap to go with a PAYG phone, live with the chance that some hacker might crack your password and screw you over. If you have a PAYG phone, you can at least go with 2 step verification. Which isn't 100% protection, but it's pretty damn solid. Again: too much trouble for hackers to bother with, when there are a million dummies who have "C00!guy69!!!!" as their password.
