I'm sorry I can't make it thru the original post.
-Any radials are better than no radials.
-Do what you can.
Here is Rudy Severns' N6LF research condensed into a powerpoint show.http://www.antennasbyn6lf.com/files/ground_system_tests.pps
N6LF has done extensive practical research which answers many questions that were debated for years before computer modeling came along Here is his main website. This is a treasure trove of info.http://www.antennasbyn6lf.com/design_of_radial_ground_systems/
OK, what the heck i'll answer the remainder of your questions:
-Always follow the manufacturers instructions for mounting height and radial installation
-It isnt' helpful to have radials with much vertical component running to the feedpoint
-Radials should run directly away from the antenna in a straight line without crossing or interconnecting, these can cause hysteresis currents and all sorts of problems
-Ground radials can lay on ground, be pinned down (super idea), or be buried to a depth of a few inches.
-Radial wire can be bare, tinned or insulated. It does not need to be staked or grounded the far end except in unusual circumstances. Radials are not intended to couple with the soil.
-If you come to an obstacle, terminate/cut your radial
-Ground radials do not need to be a specific length because they are detuned by the soil
-A few missing or short radials will not cause a 'black hole' effect in that direction
-The purpose of radials is to return the E/M flux current to the antenna
-Copper is over 1000 times better conductor than earth, so even a small conductor is better than earth, this is also why you don't need to carpet your backyard with solid copper, and why some short or missing radials are not critical
-How long? A half wavelength would be ideal. A realistic trade off is around 0.2-0.25 wavelength (1/4 wavelength), which probably also happens to be the height of your antenna on the lowest wavelength!
-How many? (personal opinion)
4-may actually be worse than just a vertical and ground rod. Makes contacts but poorly
8-Just enough to stabilize impedance; somewhat better
16-Probably the minimum you should have
32-Should have good performance
64-Quite good performance, but plenty of effort to install
120-Open your own broadcash station! The FCC smiles upon you. Engineers come to your station for ground reference measurements.