Chips like the ESP8266 or ESP32 typically only have a couple of hundred kB of RAM. Alternatively, you can buy boards with chips like the NXP i.MX 6, with which you can have gigabytes, but suddenly you're at the level of "embedded Linux" in terms of complexity, and it also looks fairly hopeless to solder such a board together yourself.

Is there a middle ground which...

* is still simple to program (... think "ESP"; maybe a simple RTOS but no MMU and processes and drivers etc etc)
* ... it also doesn't need high performance (probably not clocked a lot more than 100 MHz
* has access to a couple of hundred megabytes of RAM
	+ which doesn't need to be extremely fast, but at least a couple megabytes per second would be nice (... think "streaming out a couple uncompressed audio streams")?