Hey dude, I like my setup personally so yea those are pretty good parts
The tires will fit on your current rims (presuming the same spec as the standard TRD Off-Road which I think it is). However, you'll need some spidertrax or allpro hub centric spacers to make up the width difference. Or, get proper 4.5" backspaced 16" rims like I did and no spacers are needed.
As for the mud flaps, all mine are off. The front are too low for off-roading and get ripped off anyway... as did my rear with the 285's while on my last run at Chiva Falls... I took the other off before it got ripped off too lol. Personally I love the look without them though eventually I'm sure the 5-0 will flag me for it... eh.
As for gas millage... the bumper itself didn't seem to really do much as I could still get like 17.8 or so average with about 3/4 highway, around 16.8 about 60 city 40 highway. After the lift and heavier KM2's and such I dropped down to like 14.2ish and stopped tracking. Since then I've put the DOM Avid Off-Road sliders (heavy... just the way I ordered them haha) and the rear bumper and such... but I don't monitor the MPG's anymore lol.
If you want to man, I can take you for a ride in my truck sometime so you can get a feel for it... maybe even run out to Butcher Jones in it or something and you can feel it off-road if ya like before dropping coin.
Edit: note I have a really really heavy foot on the gas... so take my millage for a grain of salt because I drive it like I did my G35 lmao