I'm working on my third major project in this fort (the first was a 4.8 kilodorf water turbine reactor and the second was a 90 Z-level magma pump stack to move the magma forges and smelters up to the main work area) -- a downward spiraling mine track to let my dorfs move food directly from the main kitchen and food storage area to the stockpiles attached to my dining rooms.
I'd like to be able to safely push the cart down rather than have someone guide it each step of the way... But since the main dining areas are fifty Z-levels and change below the kitchens, I'm a little worried that the final stop on the course is going to measure on the Richter scale.
Ideally, I'd build pseudostops on every other level or so with a small amount of friction; just enough to keep the speed sane without bringing the cart to a premature halt. What friction level should I be shooting for?
(Also, semi-related is the /second/ spiral that's going to lead back up and draw from the same turbine to power a number of rollers to keep it going back upward. Any tips on how many rollers I'll need, give or take? Assume tracks are entirely made of built blocks for this purpose.)