i can tell you that your stock tires are probably about 40#...the stock 255/70-18 Sahara tires run 42#..as for wheels 20-30 pounds is a good guess.
You are wise in being concerned about weights.
I just upgrade my tires to Grabber AT2s 275/65-18 (i know , not much of an upgrade, they are actuially the same diameter as stock just 1" wider) but i do about 500 miles a week in my Jeep so mileage was an issue..and its not gonna be a hard core wheeler.. Its actually a work my vehicle. But I spent a lot of time looking at specs. and weights. My Grabbers are only 2# heavier then the stock tires. I stayed with stock wheels..
I see alot of guys going with big "E" rated tires...they gotta weigh a ton. Some of them get up around 65#..thats an extra 25# of unsprung weight at each corner.
From what i have seen DTs are more reasonable, compared to alot of the other aggresive tires.
But honestly the BIGGEST difference in mileage comes from your right foot...
I have a 2013 Sahara 2 door, 3.6 auto with 3.73s...i average about 19.5 with my Grabbers, that's just fine with me...
2013 Sahara 2dr BILLET, auto, hardtop, 430N, heated seats, auto temp., 3.73s, limited slip, tow pack, remote start ORDERED 2/26..Delivered 4/1
mods: Jeep 7 Spoke wheels & General Grabber AT2 275/65-18, WeatherTech liners