A 3" kit is fine, it rides great in my opinion and what i started out with but after that there is a lot more parts involved to keep ride quality...
As far as what bumper, do you mean like a winch type bumper like the LSR, ARB type??
Don't use a K&N filters they are garbage just buy a wix drop in type , and i think you should be getting a little more then 13 MPG unless your heavy on the skinny pedal as i get 13 with E-load range tires and a 6.5" lift.... There are a ton of threads about gas mileage and what you should change/replace in an attempt to get better MPG.
Some claim to get mid 20's in the MPG but i think that's quite a stretch as even stock when i bought mine 7 years ago i think i was getting 16-18 MPG
04 Jeep wj Limited 4.7 <> 6.5" Iron Rock long arms front & Adjustable lowers on rear <> Bilstein 5100's <> 285/70r17 Goodyear Duratracs <> M/T black classic lock wheels <> Addco swaybars <> Superchips 3875 <> Magnaflow Stainless exhaust <> 2 Kicker comp 12's <> Kenwood head unit.