bigredbass (and palembic too), with all due respect, I think there may be an error in your setup procedure. In your step #3, you mention setting the fret tops dead straight then tightening the truss rod to eliminate buzz. That isn't going to happen - if you tighten the trussrod(s) you will cause the strings and neck to become closer, *increasing* buzz.
It hasn't been my experience than adjusting the nut height will have any effect on fret buzz in the low frets. When you fret at the second fret, for instance, the nut height only affects the part of the string over the first fret (the part that's not speaking). Changing the height at the nut will affect buzz on the open strings, but not on the fretted ones. Although there's little buzz effect, the nut height adjustment has a lot of effect on how the playing action of the low frets will feel to your left hand. Too much height at the nut will make increase the effort to fret the low frets, too little height and the feel down there may feel indistinct. I'm not a big believer in the Buzz Feiten Tuning system, but Buzz would also tell you that too much nut height will negatively affect your intonation.
Perhaps this is a terminology issue. In the start of this thread, I believe that palembic is describing his neck relief as dead straight on the bass side and that he has backbow on the treble side. The normal meaning of this is that the neck is bowing upward toward the strings and this will indeed cause fret buzz on the low positions. But turning the truss rod nut clockwise will increase the tension on the truss rod which will increase the backbow and make the buzz worse. So, if he meant the conventional meaning of backbow and frontbow then he needs to reduce tension on the treble truss rod which decreases the force applied by the truss rod which allows the string tension to pull the neck into more relief and less buzz. If the truss rod nuts are at minimum tension, then you're out of the truss rod adjustment range and the easiest fix will be to switch to a different set of strings that has higher tension (which will create more relief). The hard solution is a fret levelling or steam treatment of the neck (gulp and double gulp).
The more conventional test for proper relief is to fret simultaneously at the 1st and 24th fret and see that there is sufficient clearance between the string and the 12th fret to prevent buzz. You also want to check to see that the gap between the string and fret tops is gradually increaseing from frets 1-12 and decreasing from 12-24. You then adjust the truss rods to create the appropriate amount of relief, where appropriate is what's right for your playing style. Generally hard players will need more relief and light players will have less. You loosen the truss rods for more relief and tighten them for less.
This test doesn't really care too much about how the nut or bridge heights are set and that's somewhat important. Although all the adjustments are interrelated, you need to have relief (bow or frontbow) in the neck for your bass not to buzz. In this test, the string is acting like a straightedge. When you fret it at 1 and 24, you're bringing the straightedge down close to the frets and taking the bridge and nut heights out of the equation.
To do a complete checkout, you want to look at the progression of gaps while testing the relief. It really needs to increase and decrease gradually and evenly, otherwise you have a problem with uneven fret tops. If the 5th fret wire is too high, the fretted 3rd fret not will buzz unless you set the action very high. You may be able to check the fret tops with a straightedge when the strings are off, but that's not guaranteed (most makers try to build the necks so they can be assembled with the fretboard planed dead flat and the fret tops with no strings dead flat and then to pull into proper relief when strung up).
To adjust the nut, you want to raise it to the point where it feels comfortable to fret the strings in the first 4-5 frets. This will vary with the diameter and tension of the strings you pick.
To finish it off, you adjust the bridge height which sets the height of the playing action. If you have a proper amount of relief set, you should be able to set the neck super low if you like that and avoid buzz. If you don't have the relief set properly then it's going to buzz even at uncomfortably high string heights.
I actually will crank the truss rods pretty quickly when I'm doing a set up. It will still tkae time to stabilize, but if you go too slowly then it takes too long to get to the endpoint. If your neck is reasonable to start with, it would be unlikely that the total change will be more than 1/3-1/2 turn even with a radical change in strings.
When the neck is being built, it's a bit of a crapshoot as to how the final neck will pull into shape and nobody can predict or know the answer until you actually string it up the first time. If you're at the unfortunate end where the tension is completely off and the relief if insufficient, you really will want to look at higher tension strings as there's not much of a workaround. A humidifier in the case may help prevent things from getting completely out of hand in dry areas, but this also may cause some action change when the instrument is out for playing, and the last thing you want is for the neck to buzz increasingly as you're playing.
