How can I get analog-in reading from Digital-PWM-out on the same board?
You are fine by doing that, but you won't get what you expect. 

A PWM signal isn't an analog value. It's a series of pulses, the duration of those pulses is set by the (not accurately called) analogWrite. So sometimes the value is 5V and sometimes it's 0V. You need to get the average value by adding e.g. an RC-filter.

Another option is to add a proper DAC (digital to analog converter) chip to your circuit.