That book looked very familiar (specially the section about moving sketches - like "I've seen and read this before) .... because I have it in PDF format. But I could not recall where I got it from. Turns out a link to it was included in the purchase email (along with the user code, a link to...
I am fairly new to Alibre as well; but if you are only looking for an Alibre solution hen I would be using STP files and "assembling" them in an Assembly (the Blue/Yellow looking brick in Alibre).
I know of other people that what you are looking at doing using things like Blender or Meshmixer...
I've found these introductory videos pretty helpful. Short and to the point (some 5-6min each). Course 5-7 are probably the most relevant for what you are after..
https://www.youtube.com/playlist?list=PL_kZpYHsPiVyRSG9o9pEl5BuUsPlj3Nbf
That is an excellent question (and one I've had as well - just out of curiosity).
I am new to this workflow but you have to think of every piece you add to the previous shape as an add-on. You are adding a new piece to the previous piece and therefore are creating a new sketch to define that...
You would be importing a file and then would have to trace/design from that import.
Supported file formats for import: https://help.alibre.com/articles/#!alibre-help-v27/supported-import-format
I do believe that the maintenance is for new versions; and that patches to the same version are still covered by your original purchase. But I could be wrong.
I've been learning Atom3D in the last few weeks; and though I've done a few other items, the Sparkfun's OpenScale enclosure is the most complete. Printed in Atomic PLA and uploaded to Prusa's Printables.
I just started using it this last week as well and it is quickly growing on me. After watching a few videos it became very clear that each feature is associated with one sketch. And if one needs multiple features then the mean separate sketches (one per feature). Sort of like building something...