Hey, first off don't split your efforts much into expansion, rather plan an expansion one shot into one thing, like APUs or GPUs only, or better results with nvidias, etc etc. rather than jumping into lets say, VEGA when both other miners have better stability or optimization.

If you want, i can help with 560/550 2gb (well most 128 bit memory polaris)
I need your help to understand something though, 560 2gb elpida (best is even unpowered ones, ie: no 6 pins) , i was even thinking of a semi asic rig, strip off useless fans, get well made chinese aluminum heatsinks and do a compact 8/12/16 builds but meh).
My problem is with cryptonight normal v7, my 560s are capped at 540-550 h/s, i'm editing elpida/hynix straps with "some" knowledge but i can never pass the 540 h/s although the memory does that with 1950-2000 mhz, whatever i do to the timings, i cant seem to pass 550 h/s even with core to 1230 mhz (1150 mhz on 16CU 560 and around 1900-2000 mhz silicon lottery on memory, always gives 500-550h/s) I don't get 550s cause they are roughly almost the same cost! and they cnat mine ethereum or ethereum forks even with 4gb of memory cause of the compute limitations.
I noticed my memory controller utilization is nearly always 50.0% exactly, can't tell what is the limitation here, cause theortically, with different timings at lets say 2100 mhz, memory should produce some 5-15% more hash rate correct?
I'm glad to share any info with you i have 6x 580/570 4gb (hynix ajr high quality), 2x580 8gb Hynix mjr (1100 h/s CN heavy), 9xRX 560 2gb (elpida/hynix with mixed factory 1750mhz memory batches "not silicone lottery here") and 2x 560 4gb Micron mining mostly cryptonight forks. at high efficiency (specially when compared to the wasteful eth)