For a first LFS, you’ll have an easier time doing it for a more standard machine first before doing it for a quirky SOC with a lot of custom hardware. Especially if it’s your first time, it can be tricky to determine if something breaks because you haven’t done it before and you missed something, or because it’s a different CPU, or your cross-compiling toolkit has some problem, or whatever else. It will take a while to build some things and you’ll have to deviate from standard LFS for the bootloader and image format, you’ll have to add some of the CPi-specific bits for hardware support (like the gearbox if you go with A-06, drivers for the fan, printer, etc.).
That aside, I’ve been playing with ARM stuff for years and I love ARM (and the A-06 is wonderful, I love it), but so far, riscv64 is really nice and compiling stuff goes a little smoother. The chip’s less beefy than the ARM offerings by quite a bit but RISC-V is open (so dev support is pretty enthusiastic) and there’s so much variance in ARM that the R-01 goes a lot smoother when compiling anything.