I'm with Natwest too, have no idea what that little calculator they give you does, I can only assume its for working out how little interest they're going to pay me this month.
I'll ignore the age-old thread and wrong location and answer anyway.
1. Moto trials brakes use a smaller diameter, thicker disk with a larger piston meaning braking power is stronger. The larger piston has to be closer to the rotor for it to work with the same amount of lever pull.
2. Spoke flex on 26" bikes is an issue, makes the back end feel less precise and more 'loose'
3. It puts a load of weight out the back of the bike which isn't ideal.
4. Larger wheel = more turning force and the less able the rotor is able to deal with it. so fine for 20", but the extra leverage of 26" wheels makes it a less effective brake
Have you tried squirting WD40 / GT85 / Penetrating lube into the lockring gap to loosen it up? Might be worth a try before you try to dissassemble. If you do take it apart, watch the bearings - They are loose and may fall under the fridge with the old sweetcorn.
Pretty sure the official answer is yes to everything. Only debateable one is the headset to frame interface; some like it dry, others prefer a bit of grease.
I put copper anti sieze grease on freewheel and cog threads.
EDIT: Sorry, I'm not a professional (though have worked in a bike shop?)
Kenda small blocks are dogshit for grip.
My experience (riding alot of natural of different sorts, in the wet etc) from best to ok:
Rear:
Continental Der Kaiser / Rain King
Maxxis Highroller 2.35 dual ply super tacky
Try-all Stiky 2.5
Front:
Try-All Stiky
Maxxis larsen TT 2.35 super tacky single ply
Maxxis Highroller 2.1 eXCeption series
Try-all and Maxxis have the same compound. Maxxis wins on the rear as it rolls (side to side) less than the rounder, wider stiky.
Maxxis and try-all up front are similar grip wise, try-all is lighter and bit more precise as its narrower.
Actual splined cranks: Take lock ring off, use a mallet and penetrating fluid.
Threaded / screw-on cranks: Take a look on the Tartybikes website for video help.
I seem to remember Ali did one up his way on his Koxx Mixx (i think?) where you ride xc, dh, and some watered down trials on the same bike and it makes a total score.
Oh jesus its 1999 again.
A harsh grind, no booster, a toed in pad (Rockman, TNN, whatever)and ever so slightly loose bolts will make a loud, but shit brake.
The best brake I ever remember having was a smooth D521 with original Plaz CRMs cleaned with muc-off. However, it was the best brake for about 20 minutes riding street until either a bit of dust landed on the rim or some light drizzle came. Then it was useless.
Needless to say I have run a grind for the past 6 years.