You know what I like about conversing with you? You've barely just jumped in with both feet but I think you secretly have a streak in you that is the hacker ethos.
You want 8GB? Pffftt! Stop thinking so damn small! Get a decommissioned HP EliteDesk 800 Mini Gen-whatever, slap some multi-TB SSDs/NVMes & fill it with 16 or 32GB. OWRT runs on x86-64!
Seriously though, the single biggest problem with building your own OWRT AP isn't the CPU/SOC. The Intel N100, N200, N300-series SBCs are pretty close to the same the power drawn as ARM's latest. The biggest problems are the blasted chip sets of the Wi-Fi adapters. Again MediaTek seems to have the better reputation but as I've stated elsewhere, I loath Wi-FI; gimme good ol'Cat 6+ any day of the week.