spindle preload and lube

Generally, all the preload will have been built into the assembly with spac ers and/or belville washers. So, "Darn tight" is just about right.
As far as lubing ball bearings, the general wisdom in the Logan Lathe group is that you shouldn't fill them more than 1/3 full of grease, or they will run way too hot. Also you should be extremely careful when cleaning them - as a matter of fact, you shouldn't clean them at all unless there is an ex isting problem. Cleaning is best done with as little agitation as possible, and absolutely no ultrasonics or air guns. You can make a good bearing bad in a hurry by mishandling it during cleaning.
So, if the bearings turn OK without clicks & rattles, you may just be best off to leave them alone. If they do click, it may be due to dried up grease , and there's nothing to lose by cleaning them, but you may find that after cleaning & repacking that the bearing is cooked anyway and needs replaceme nt.
All this is, of course to be taken with the usual grain of salt and, if you 're now comfortable with disassembling the head, you can always use the bea rings as-is and replace them later.

And, further to the "never use an air gun on a ball bearing" admonition, th ere is a case when it's highly desirable to do so: In a motorcycle shop whe re I used to work, we would save up otherwise bad bearings for later entert ainment. The procedure is to wash out all the lubricant, hold the inner rac e with thumb and index finger, direct an air gun at the balls & outer race and get it spinning as fast as possible. Then you put it down in the parkin g lot. Those little guys would run many hundreds of feet in a hurry.
Of course all this is made even more entertaining by copious application of beer & bourbon to the participants.

I believe the nut tightness has no bearing on the preload (unless absurdly tight) as it is clamping on a solid metal stack of bearing races and spacers, and as you note the preloads are based on those spacer and bearing race dimensions. The tolerance on precision bearings should be tight enough that no changes in spacers are required. As for lube, I'd ensure you pump a suitable amount of the normal spindle lube in before running the spindle, and I'd start at low RPM and work up slowly over time as you find in the spindle break-in procedures for most spindles.

Barden has recommended torque for preload nuts in their literature - the numbers are pretty big. I recently purchased a hook spanner with a 24" handle to assemble the 160mm ID bearings in the work drive for a new gun drill, and even then probably didn't meet the spec.
Kuber Isoflex NBU 15 is a safe choice for the grease. You can purchase a small tube from these folks, or direct from Kluber in NH.
Barden also has info on the qty of grease based on the bearing size. I use a syringe with a blunt needle to gage the amount, and to get the grease squirted in between the balls before run-in.

I did this once, spun up a bearing on my finger. I was gonna let it run down the street. But as I was spinning it up I noticed the pitch of the sound it made getting higher and higher. I kept spinng it up until the sound got too high for me to hear. A fraction of a second later the bearing blew up. I thought my finger was broken too but it was just really sore. Scared the poop outa me. Eric

As well it should have. You're damned lucky you didn't lose those fingers. Bearing retainers are an awful lot like chainsaws when spinning at 20K RPMs.

What would be worse is if it suddenly seized-up and twisted your finger off.