ESPRESSOBin Ultra: First time user

I'm trying to install openwrt on the espressobin ultra, but I'm not really sure where to start. The installation guide includes installing a new dtb that isn't included in the built files (which seems to mean I'll need to compile the kernel myself and I'm really not in the mood of that). Also, it seems that I'll need to flash a new U-Boot?

If someone could give me a bit of guidance here (or even just point me in the right direction) that would be fantastic. I really want to use openwrt for this project of mine (the ultra was the only cheap and small router I could find with five gb-ethernet ports), but it seems like it's a bit more complicated to install than I've anticipated.

Thanks in advance.