yup i am at oem filter now.turbo kit has its own filter.its complete kit.imported through maxpower guys.they will install it.unluckyly good tuner is not here.so live tuning will be done from abroad charging 480$! yup that sucks..
about your question.i am getting upto 24 km/Lwith light foot in city in ongoing traffic.but in traffic jams and stop & go traffic average is near 20. coz battry dont get charged with low speed breaking.at 50-80 km speed honda fit can really give 25 av.
on motorway gives upto 18.
i have few tips for fuel average. which i will share.its hard to type from my cell.
for your transmission question,
i have triptronic transmissionfor
there are turbo's for cvt and auti trans too.man honda fit aftermarket is huge 
i am also changing injectors to 410cc acura RSX type s,iridium IX spark plugs,AEM-FIC-6,exhaust,tranmission cooler etc etc
lets see how much my average drops after that..but it wont matter coz i have not imported this car for fuel economy anyway