I getting a new red fit 1.3 from PI. the basic model, Pi gave upgrade to 15'' Rims/tyres and i requested a Mugen body kit. Help me decide,

1.Shall i upgrade more to 16'' rims and tyres, thinking about getting adventi rims, preferably light ones ? Should i jump to 16'' ?? Bigger rims means more fuel being drunk, how like this ? 15 or 16

2.Shall i install the Mugen bdy kit ? i know it takes up some weight. i prefer bdykit with 16'' rims, but afraid of the FC. bdykit with 15'' rims is another alternative, not too sure if i just simply upgrade the rims to 16'' without any bodykit.

Help me guys, so that i can make a better decision.