Class III for Europe? Or Canada?
For a Class III device for Europe the Technical File is typically called a Design Dossier. The term "Technical File" is usually reserved for devices in all other risk classes.
There is essentially no difference between the requirements for the two sets of documentation, but one way I tend to distinguish it is that a Technical File submission can make reference to records stored elsewhere, that could be submitted upon subsequent request. A Design Dossier should be stand-alone, thus could be several volumes in total.
SGS would typically take 0.5 - 1.0 days to review a "standard" Technical File, and 2-4 days to review a "standard" Design Dossier (resulting in an EC Design Examination certificate as per Section 4 of Annex II).
Naturally, there is no such thing as "standard".
There can also sometimes be a wider range of devices covered by a Technical File, you get a lot less flexibility with Design Dossiers, which tend to need to be very product-specific, or at best, range-specific / dimensional-specific.
In terms of content, the GHTF STED and the NB-MED guidance on Technical Documentation are your friends.
In addressing your specific concerns, I would suggest for a Technical File, a simple flowchart (maybe 5-10 steps), giving a strategic description of the manufacturing process should be fine. You should also identify key subcontractors, suppliers, outsourced processes etc.
For a Design Dossier, I believe you should be as detailed as necessary/possible. You may want a "strategic" flowchart, as above, giving a basic overview, as well as a fully-detailed process map.
In terms of what changes you need to notify...how long is a piece of string?
It's almost impossible to answer this question.
What I would always advise is that
a) you identify within your system changes that would be obviously significant
b) that you contact your Notified Body (email or phone) to discuss grey-area changes. It may be that all they feel they need is communication of the change, and that no further action is required at that time.
c) that you record all changes that you unilaterally deem are non-significant, or that you are advised by the NB are non-significant
Best Regards,