They (older Arduinos) are never useless… just a little harder to get started with (for IoT, but a great teaching experience), and great for experimenting with. None of this worrying about 3.3v pins, metric-butt-ton of GPIO in the case of the MEGA… slower than current gen, yes, but still plenty nuf power and memory for IoT and even robotics.
It’s taken you 4 days to get to the point where you really start having fun.
Order a NodeMCU for a few $ and you’ll be up and running in a few minutes without the need for any wiring. The little board will just sit there and do it’s job and you’ll be able to do things like update it wirelessly and interrogate it for its WiFi signal strength. It will also be processing your code faster and have more memory for running your sketches.
You won’t want to go back to your Arduino and ESP-01 after that, and the Arduino will be consigned to a drawer where it gathers dust - unless you’re name is @Gunner of course!
What can I say, I is ol’skool … I still have a 4WD rover using UNO & ESP-01… that is all it needs and saves my ESPs for other tasks. And nothing beats my MEGA & ESP-01 with large GPIO availability for messing around with.
I always go back to UNO when testing new concepts or sensors (new to me) . . . it has a decade of support, libraries and examples . . . once I get the basics working on UNO I migrate to ESP, then Blynk as a final step . . .