There maybe some here who will have advice on suspension. There is also a member, see CraigB and his thread
ECU reprogramming in
ENGINE BAY who probably can give advice on what performance mods can be done with stock ECU, and what would require after-market ECU.
Regarding the suspension - I realise the i20 is a different platform but Hyundai has i20s in the WRC - could that be a useful starting point for research?
I am discounting the Hyundai 'N' sub-brand that will apparently start with i30 (Elantra GT) based on WRC knowledge (the N brand is based in the same town/city as Hyundai WRC HQ) - as a) it isn't, seemingly, released yet (so likely details like suspension aren't available); and b) 'gravel suspension' and suspension you put on a 'hot' hatch for production purposes are probably not going to be the same.