ok I'll answer whatever questions I can. As for whether they can be mounted on the stock bumper... I won't say they can't, I will say I don't know if they will. PIAA does not list the 520's as compatable with a stock Explorer but that certainly doesn't mean they won't fit. They are not as deep as most other lights I've seen so it shouldn't be a problem, but try to check it as well as you can before drilling. One of the cool features of the 520's is a tilted tightening bolt, so hypothetically you could drill a hole into the front of the bumper, stick in the bolt straight horizontal, and tighten it down and it would work... might stick out but it'd work
. The package you get from PIAA will include everything, relays, wiring, switch, light covers, everything. The wiring is all pre-assembled so its the easiest lights I've ever seen to hook up. Here's the instructions I follow. Attach the white wire loop to the positive end of the battery, attach the black wire loop to the negative side of the battery, hook up connectors to lights that you've already attached to the bumper, the connectors are set up so you can only plug them in one way. Then bring the switch wires through the firewall, hook up your switch to a fuse (I use my radio fuse so the lights only come on when the car is on, even though I know it's not the safest way to go), attach the black switch wire to a ground (any screw down in that area will usually work but you can whip otu the voltmeter if you like), attach the switch to wherever you want it to be, and voila, lights are installed. THATS IT!
As for the 9004's, I think there is a difference but some people have different experiences. Some say they make a great difference, others say its just kind of noticeably different. I don't know pricing on these lights but i recall seeing them around $70. They are 50 state street legal.
Another point... if your going to be on the Colorado Fall colors run, you'll get to see a wide variety of PIAA's. I've got 520 fogs, 80 XT driving, 9004's, and 1500 clear fogs. By the time of that run I may also have a few other different varieties. Rick has the 80 XT drivings. Ray Lobato has the 520 Driving, two sets of 80's (one set 80 fog, one set 80 driving). If Dignan has installed his PIAA's, then you'll get to see another set of... umm... I can't remember if he got the PIAA 60's or the PIAA 40's. If Brett is going you'll also get to see the PIAA 1500 clear driving. And if Guy is going, you'll get to see either 60's or 40's I don't recall which one he has. As far as I know thats all that will be there with PIAA lights on.