Hi HannaBanana: I just went through the same exercise this week, so I happen to know the answer for the hardware half of your problem. You are correct the MAX232 boards need a 5V level signal, so you first need to shift the 1.8V signal up to 5V levels. I used this board https://www.sparkfun.com/products/11955 . My system only needed data going from the 410c to the device, so I have only tested the level shifter in the Tx direction, although I have no reason to believe that the Rx won’t work. Once you get the IOs from the 410c up to 5V levels you can then drive the MAX232 board.
The other half of your problem is getting the uart0 port enabled. On Linux this required some changes to the kernel and the device tree to enable the port (I think this should have been the default in the released kernel, but it isn’t). I tried building the new kernel on the 410c but for some reason it can’t start the GPU. When I built the kernel on a x86 Linux box it worked.
I am not sure if uart0 is enabled in Android or not. I’ll leave the remained of the software part of your challenge to someone more with more knowledge than myself.