Warning, I'm going to unload some experience to save you money, this might take a few minutes to read but will save you money that took weeks to earn.
The K&N doesn't work as well on the first Gen Tundra. I have it, I went back to stock, and recently I decided to give it a second chance. I need to be clear, I'm giving it a second chance for two reasons. One, I have 4.56 gears now, the reason that matters is the K&N lowers low end torque(bring on the "no it doesn'ts"
) which is what trucks need to have. It exchanges that low end torque for upper end horsepower, which you rarely utilize in a truck. Reason two is, I've been contemplating putting fiberglass front fenders on, and if I do I'll likely put the K&N to use since the stock intake may have a problem with water getting kicked up to it(fiberglass fenders require removal of the plastic liner that keeps water out of the intake tube).
In short, the K&N intake tube doesn't really help, I paid close to $300 for it and was very disappointed. Right now it is working well for me, but that is because my 4.56 gears multiply torque to even out the loss from the K&N. Also I do mostly highway driving now, and it seems to help slightly when I need to pass somebody. That Jet thing doesn't work on first gen Tundras, what works on one vehicle doesn't necessarily work on another. Toyota didn't leave much room for improvement. The fact is, if the supercharged Tundra could breathe through the stock intake, your stock 4.7L won't have a problem breathing through it. Save that money, get headers and/or get an electric fan kit.
I've played with my exhaust enough to learn the hard way. No exhaust system/kit is worth getting for power/mpg improvements. The stock piping was brilliantly matched to the 4.7L's needs, the only restrictive sections are the manifold(header), the Y pipe(not as bad as people think as far as HP reduction), and the muffler. Take my advice here, all you want to do is get a muffler you like and use it to replace the stock muffler and resonator. Keep the stock piping in place including that Y pipe. If you want headers, get a set of short tubes and call it a day. I've ran my JBA's for almost three years with no problems. I've heard good things about Gibson and Borla mufflers on Tundras, but the only mufflers I've ever liked on these trucks are Spintech and the BAMuffler. I run a Spintech Prostreet muffler and it sounds awesome, no drone and I can't hear it on highway trips. I've met a few guys with the BAMuffler and it's the only other muffler I'd run on my truck. A guy named Keith makes those, I can put you in contact with him if you are interested. Keith is a great guy and his work is second to none when it comes to mufflers.
That hood with the scoop is available, I can't recall who makes it but I want to say Outlaw.
The diff breather is a good mod, what you do is remove the stock differential breather, replace it with a barbed fitting. I got the fitting from a Nissan dealership, I can't recall the part number but if I find it I'll post it. I put the barbed fitting on, ran a flexible tube up to an area where water won't reach, then put a small air cleaner on it. That way, if I'm ever crossing water that is deep enough to get over my diff(20"+) my diff won't suck water in. The idea is, water will be colder than the differential casing/fluid and can cause the air within the diff casing to contract rapidly and suck in water. Extending the breather by running a tube provides a snorkel effect, eliminating the chance of getting water into the diff. Another benefit is, it's hard to plug the air cleaner I used, limiting the chances that my diff will stop breathing and blow out an axle seal.
If anybody cares do disagree with me on anything, feel free. I don't mind sharing how I know what I've learned. I've installed every part in my sig line other than my window tint and gears(that's black magic stuff) so I'm very aware of the way my parts work. There aren't many on this forum as prone to modifying their first gen as myself, I've learned a lot and want to help people put money in good places. Thanks for the nod 06dblecab, I agree the superchager is the only serious power mod for these trucks. Damn nice truck you have too.