You should assume that 1x risers are not supported. It's already been made quite clear the acorn is not going to be useful in that situation unless you run it by itself, not talking to the GPUs.
PCI-e v1 should work fine if your board provides 8 lanes to the integrated m.2, or you can use an 8x to m.2 or 16x to a dual m.2 adapter, plus your slave card(s) are in 8x slots. The math is really obvious and simple -- if you want to use half-speed pci-e from what is suggested, then double the lanes. If you use pci-e v3 it doesn't speed up the acorn so that will still need x4, but the video cards could get away with 2 lanes. There's no reason you should ever need a 16x riser to the video card!
I'll try to figure out which algos are which state 256/512 but it's more complicated than that - you should expect a 1060 to get a bigger boost than a 1080 Ti, for example.

lyra2rev2 - 256 bit
lyra2z - 256 bit
neoscrypt - 256 bit
equihash based (zhash etc) - 256 bit
cryptonight based (v7, heavy, light) - 256 bit
phi1612 - 512 bit
x16r/s - 512 bit
phi2 - 512 bit
x17 - 512 bit
tribus - 512 bit
skunk - 512 bit