Hi Paul
Welcome. Thanks for your interest, and hopefully purchase later on of Lumion.

As a covering note for your questions, some things will change when you get to use the Lumion 8 Pro Trial.
To answer your questions:
1. File Saving:In v7.5 the Scene data - that is the things you do to set up a Scene with Photos, animations and entourage as well as the placement of Imported Models gets saved to a Scene file. By default that's in the Documents folder. There is also the option to do a save to LS7 Save Scene and Models that can be saved to any folder. Those options are historical, but essentially both do the same but for different purposes.
Imported Models are saved when imported or updated via a
Reload. Those files by default are also in a folder in Documents (Documents\Lumion 7.0\Library)
That changes in V8 for the Scene data. Imported Models still follow the process as in V7.5, however when saving a Scene the user now has just the one option, to save an LS8 file. That file is basically the same as the LS file in V7.5, ie it saves the Scene data and the Imported Models in one file. You can save that file to any folder.
2. Templates:Yes to both of those. They are not referred to as 'templates', but you can make templates with entourage, Photos and Effects, movie animations and effects etc. We have users that do that, then basically drop their building design in to the 'template' file, do a few tweaks, and press the render button

Any file can act as a template when updated and saved out to a different name.
Pro users also can use the
Merge feature to merge content from any other LS file.
3. Model Updates:Yes. You simply select the mode and press the
Reload button. It re-imports the model for changes in the model and materials and retains materials you have already worked on.
Sometimes users need to save out the model to a new file name for versioning purposes, so all you need do is us the
Reload From New File to again update your model.
4. Materials List:There is no list as such. You only need to change those surfaces where you want to. That is, it is not a process of having to change all SketchUp materials to Lumon materials. Material - color and texture settings are transferred from SketchUp. You can then decide if the surface using that material would benefit from converting it from an
Imported Material to a Lumion material.
You might decide to do that because you would prefer a different texture and a Lumion material has a better or higher resolution texture, or that the gloss and reflectivity of the material needs to be stronger or weaker that is applied as defaults for Imported Materials.
You work your way through the model by simply selecting a surface. Lumion optimises that process by merging all separate surfaces from SketchUp that have the same material name in to one new surface. This makes it fast to apply changes to a combined surface than perhaps having to deal with 20 or 50+ small separate surfaces.
5. Material Indicators:As in 4 all surfaces start as an
Imported Material. When you select (click on a surface), and it has not been changed to a Lumion material then it shows as an
Imported Material.
There is also the option to save and load a special materials file called a
Material Set. This saves all Lumion material settings, and when loaded does show as a 'list'. You can also use these to apply materials to other buildings that share the same material names. That can make it very fast to apply your standard materials across various projects.
Some users use it also to 'template' their materials workflow.
6. Magic Curtain 
:
The prime reason is to assist in protecting our paying customers at the Support Center. We do however also allows Trial users access, and split up educational and commercial users to different sections. It allows us to also identify the different products and versions that someone might have so we can better target our support and replies.
So to answer your question: all the topics in Boards where users/members have asked questions, plus Wishlist topics, and Assets and Resources topics. We make available support information for common topics in our open Knowledgebase Articles, but there can be a wealth of answers at your finger tips via 2 search tools as well. Boards include those on Importing Models, General, bugs and errors, license and reset and download and installation etc.
Hope this answers your questions.
Let us know if there's anything else we can help with or further clarification or other questions you have.