1GB is probably enough to run one basic service without a GUI. If you want anything more than that you’re going to probably end up running out of RAM and hitting the SWAP file–grinding everything to a snail’s pace. Useful projects here might be to add smarts to something dumb around the house or making an old printer support wireless printing via cups.

Like others have said if you want to tinker, a virtual machine via virtualbox or VMware is free for your use case.

If you strongly prefer hardware, an old PC will probably be cheap or free.

If you really want a pi you’ll probably have to look for something that has at minimum 4Gb (which will be easy to outgrow), recommending 8GB+. Note that raspberry pi’s run best on the official power plug as a USB-a to micro/c won’t provide enough power to be stable and will cause weird issues or crash the pi under heavier loads or when drawing power from the pins.

I googled the echo flex and I don’t see any evidence someone has gotten the bootloader unlocked or have been able to install a custom ROM/OS. Depending on the generation the flex is based on, it could be Linux or android based. Have you been able to access the os on your devices? If not, you might have a lot of work on your hands to get enough access to install any kind of non-stock OS.