Q. What features I can add aftermarket on Nexon XZ variant? which are available on XZ+ variant??

Central Arm rest, engine Start stop button, back arm rest and cupholders, rear window defogger, alloy wheels, tyres are a bit broader, keyless entry. I would suggest you to Go with the most running XZ+ variant it has all the features

Can I add push start button on XMS variant Nexon

Adding the XZ+ features to XZ variat, I think expensive compared to buy XZ+.