Correct me if im wrong, a king pin bearings are just a tapered bearing
When you bolt the king pin down it pushes the bearing into a sleeve on your diff
It tensions by doing that I assume

The get the tension right you need to add/remove shims on the kingpin

Undo the four bolts and JUST pry the kingpin up a few millimetres to check if there is a shim (or two) fitted before you get carried away...
Kingpins are a service item and are usually installed with a shim or two.
As the bearings wear, as shim is removed to correct the preload on the bearing.
Not many (non suzuki) mechanics have spare shims laying around so if they get a car in for new KP bearings they usually don't have shims to replace.

If your car has shims you remove one at a time from top then bottom. Check the hub still swivels smoothly with no notchiness or play after removing each shim.
If your car has no shims and has play then your KP bearings need replacing and new shims should be acquired.

While we're talking about kingpins, if one was to have a wobble which he/she thought may be related to these, how long could it be left without fear of major damage (this does not include damage caused by loss of vehicle control :p)

In other words, if I've got a leak and a wobble in the front end of my zook, would it be worth doing all the bearings and seals and kingpins and knuckles and hubs at the same time?

Then all I'd have left are the rear wheel bearings and it would be aces!

That bit i get, but, how do I know the tension required. All the written stuff I can find just says tension with the use of shims. Means fuk all without knowing tension.

Where or how do I tension, using a rattle gun, tension wrench, on the 4 retainer bolts ??????

Just saying add or remove shims is about as usefull as a boil on the arse.

While we're talking about kingpins, if one was to have a wobble which he/she thought may be related to these, how long could it be left without fear of major damage (this does not include damage caused by loss of vehicle control :p)

In other words, if I've got a leak and a wobble in the front end of my zook, would it be worth doing all the bearings and seals and kingpins and knuckles and hubs at the same time?

Then all I'd have left are the rear wheel bearings and it would be aces!

C'mon man that's just verging on dangerous and is hell dodgy!! I'd take the vehicle of the road as fix those bloody faults before it does get real bad and you loose control of it. Excuses like can't afford it atm, don't have the time, need the vehicle are all invalid as if it does cause an accident you'll be up for a lot more than just a swivel hub rebuild kit and a day off the road.

If you have a leaky knuckle, diff oil is generally passing through the axle seal and entering the knuckle and breaking down the grease. You'll have to clean all the crap out and re-grease it thus everything has got to come out anyway. The knuckle rebuild kit for both sides is ~120ish and replaces everything except the wheelbearings.