⦠thanks 
would be nice to have a chance to have some kind of āconsultingā place here, but I am afraid I would have spammed your thread with questions 
(so - instead - I“ll try to ask one-by-one, as I go, in separate thread(s) of mine, glad for any possible feedback)
but - just to add - concerning matte-tutorials in general -
what I find most difficult when trying to learn some fundamentals of matte-painting is finding some more matte-specific information on the pipeline/production process, the daily routine of a matte-painter, the way matte-painters collaborate with others in a team, their part in the pipeline, wheather (or to what extent) a matte-painter needs to know also compositing and/or other techniques or packages; what are common mistakes beginners might do - and should avoid - not to make the workflow difficult for other people in the following process, and so ..
in other words - people (incl. me) new to matte-painting, but not to PS (using PS on every-day basis for other different image post-processing tasks) do not actually look for general PS technique kind of "how to use PS Curves", but - instead - would like to know - for example - wheather to apply/or not to apply grading, as this is a compositor“s task (is it???) .. or -
not actually looking for the info on "how to extract objects", but - instead - whether (and why, if so) it is important to keep keyed out objects in separare layers (maybe for a compositor?? or for some other reason?) - or - whether a simple-layered flat final 2D painting is just fine - and what is going to happen to the matte-painting next ...
(sorry, just silly examples comming to my mind right now .. )
I am trying to say - I am not very successful in finding some basic production info, I mean kind of "what" or "why" matte-specific answers, instead of "how", which I am not seeking that much, actually ..
but - that is just me,
since - as Cyberone mentioned - "how" answers are important too,
so - any kind of insight into the matte-techniques might be fine ..
a.