I don't have all your answers, particularly I don't have a good understanding of what Tone Mapping actually does - in principle, it tries to give you more color information in the output than you'd get without it.  Basically it helps you avoid the brightest parts of your image from blowing out to completely white, and the darkest parts from going completely black.

Preview Hardware Shading (actually available in Poser 7 also) - if your graphics card supports the features it requires - will give you more accurate preview when dealing with complex materials, particularly stuff like Blender nodes.  With it turned off, you won't see the result of any Blender nodes; with it turned on, you'll get a pretty accurate preview of what they look like in the final render.

According to Stefan Tewer (stewer, the guy who wrote the renderer) Light-based Ambient Occlusion (that is, when you turn on Ambient Occlusion on a light) is skipped when Indirect Lighting is turned on.  Material-based Ambient Occlusion (that is, when you have an Ambient Occlusion node configured for a given material) is still processed, but incurs a heavy computation hit when rendering with Indirect Lighting turned on.  In many cases, you may find you don't need to use AO when working with Indirect Lighting, as IL does similar things but in a smarter and more realistic way (ideally).

Indirect lighting is neither a new kind of light or a material, it's a render setting.  It is more commonly referred to as "Global Illumination" in other rendering apps.

You do not NEED a full panoramic scene to use Indirect Lighting, but imo for indoor scenes you really should have an enclosed environment.  If you have, for example, a floor without walls or ceiling, most of the light will go from whatever light sources in the scene, to the first surface it encounters, and bounce off of it - and then vanish into the empty universe surrounding it.  This really defeats the purpose of using Global Illumination techniques.  Outdoor lighting is a different matter, and in those cases you'd probably want some kind of sky dome (Bagginsbill's environment sphere for example) to be your main source of light, to get good results.

Yes IL can be adjusted for intensity (with Dimension3D's render interface script), although keep in mind that you're seeing early results from people with bad habits that stem from older versions of Poser, where you had to have a bunch of fill lights or IBL to avoid having parts of your image be completely black due to the unrealistic way lighting was handled.  This is just technique, and as people get more comfortable with the results that come out of the renderer with IL enabled, you can expect the over-lighting you're seeing to get better.  You can adjust it if you really want to, but imo it's probably better to adjust the lighting instead.

Bagginsbill's environment sphere prop emits light by plugging color into the Ambient_Color and value into Ambient_Value channels of the sphere's materials.  This works the same for any material anywhere in your scene, if it has Ambient color and value information, then it will emit light that Indirect Lighting will cast around the scene.  This is a standard feature of Global Illumination in other apps, and can give you some very interesting results that were pretty difficult to obtain in older versions, like the famous "bioluminescence" thread.  Now instead of having to set up Gather nodes everwhere you want a surface to be illuminated by a glowing material, you just make the material glow.

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