"Attack" and "Release" can mean different things to different limiters. In Pro-L, the limiter separates transients from the incoming signal and handles them differently than the main body of data. The attack and release controls determine when the secondary algorithm kicks in.
"Release" is also a variable parameter in so-called "intelligent" limiters such as Ozone's. These types of limiters attempt to automatically adjust release times based on the nature of the incoming signal, giving a quicker release for transients and a slower release for slower-changing levels. This helps to preserve transient perception despite your best attempts to smash the life out of them.
Clipping and saturation are codewords for harmonic distortion. If the limiter makes abrupt changes to levels, letting the signal get right up to the limit before taking any action, you get flat-topping and the harmonic distortion that comes with it. If your goal is transparency, you want settings that allow the limiter to minimize distortion (and potentially aliasing). But sometimes we use limiters for "color", meaning distortion, in which case a clipper is just the ticket. If a limiter doesn't have a clipper, you can emulate it by using very extreme settings (e.g. Ozone's "fast and loud" setting) and setting lookahead to zero.
Stereo linking means that you always lower both channels equally, even if the event that crossed the limiter's threshold was only on one side. Without this, the stereo image can bounce around in an unnatural way as one side gets reduced but not the other, causing center-panned instruments to appear to move out of the center.
Unlinking the two channels makes most sense on individual tracks and sub-busses, where shifts in the stereo image may be acceptable or even desirable. Unlinking can result in a wider image. More sophisticated limiters let you adjust the amount of linking rather than just turning it on or off. Pro-L goes the furthest with this concept, letting you adjust the amount of linking separately for transients and non-transient material.
As for preferring a limiter's built-in dither over SONAR's dither options, that's just a personal preference. As I've said often, your choice of dither algorithms is almost irrelevant, certainly one of the least-important decisions you'll make. See for yourself: try every dither option you've got and see if you can tell any difference. I don't think you will.