18' is a really good size for the Bronco and any other vehicle that might need to be trailered. Brakes on both axles for sure, some don't have that. You'll be okay with the standard width, most of the fenders will flex enough to allow you to get past them if needed. If you push them out enough times you or a friend can always weld braces under to help hold them.
Tying down, what a can of worms, anything will work, but here's what I do. I had axle tabs welded on and use 2" straps directly inline with the tabs about 2' in front and rear of the Bronco. Why? This method allows any size tire or modification to be used. Strapping the suspension down to a point of bump stops is hard on the suspension and totally unnecessary, why? You don't want the Bronco to become part of the trailer suspension because for the most part the trailer doesn't have suspension, just axles with no shocks. Making the trailer suspension absorb the weight of the Bronco just wears the hangers and tires out quicker. You don't need the tabs, just use the axle straps to get under the brake lines. If you strap your Bronco this way, as you go down the road the Bronco will rock and bounce utilizing the shocks and suspension just as though you were driving down the road, not bouncing up and down like an empty trailer. I don't like the straps at an angle because if one of those break and you don't know it, it can cause the Bronco to creep to the side of the good strap and I see a potential disaster in an accident. Strapped directly down to the trailer, in an emergency situation, the axles will stay planted to the trailer even if one front and one rear strap breaks, period, not so with the other methods mentioned.
Did you see the post from David, Jamey and Steve with the 38' trailer on their recent trek to the Rubicon? All three strapped down by the axles and never moved. Good luck!