Bitcoin Full Node + Lightning running on single-board-computer, possible?
Please take a look at pine64.org. They have the Rock64, which has a quad-core A53 ARM 64-bit CPU; up to 4GB RAM. And I have heard they will release a new model with a hex-core CPU soon as well. I have used the Pine64 (original 2GB model) for simple Linux experimentation; installed Ubuntu on it, etc. Have not tried Rock64 yet, but am planning to.

The ODROID XU4 may work well too, although I have found with my VPS full nodes, that 4GB of RAM is helpful... see: http://www.hardkernel.com/main/products/prdt_info.php?g_code=G143452239825