Sharepoint 2013 Libraries

Question

We are looking at how best to design our Sharepoint 2013 and I have a few questions re Libraries.
We are a Public Sector business- and have 7 main Business areas (Adult and Children services, Environment, Transport, etc.) I am considering that they each have a site collection and each department in each business area has its own team site. Adult and
Children Services (ACS) have an Adoption team so we would have a Site Collection for ACS and Adoption would have a team site.
I'm wondering if the following is possible:
Each Team Site will have one or more libraries specific to its needs. So Adoption Tem Site could for example have 3 Libraries: Adoption Applications / Adoption Policies / Adoption Case Files (I'm making these up but hope it makes sense). One big reason I
am considering this set up is because the business currently use government defined taxonomy and this is how the current document file plan is structured. So users are familiar with putting docs in correct folders however I am not suggesting a library is created
for each folder but rather for each major category.    
Scenario 1: User creates a brand new doc using MS Word and then drops it into the Sharepoint team library.
Q1: Is it possible that the library can restrict docs being added if they do not have mandatory tags applied? I.e. can libraries be created that restrict what can be added? For example you can’t add a document to the library if an Adoption Application case
worker has not been assigned.
Q2: Is it possible that when a doc is added to a library that Meta tags are applied automatically to the doc based on predefined tags for that library. So for example if I drop a doc in the Adoption Applications library then that doc is assigned a specific
taxonomy classification, id sequence value etc. This means users don’t have to repeatedly assign tags.
I know the ideal is to use to doc templates so that correct docs are used and correct attributes defined. However (even with Governance to say not to) it is possible that users will till try and create docs from scratch and put them in the libraries. 
I am trying to minimise user input when adding a doc to a library.
Q3: Are libraries the right way to go (remember users are familiar with existing taxonomy and folder structure).
Q4. Is there a rule of thumb as to the number of libraries on a team site?
Q5. IS there a max capacity for a library?
Q6 Can permissions/restrictions be applied at library level.
Q7. Can a library be made accessible to another team site?  Ie can a library be ‘shared’ across team sites?
Q8. Can the action of dropping a doc into a folder trigger a basic workflow?
I know there are a lot of questions – I am researching this topic but thought there may be people who have experience and could give some advice. Any help is really apprecited.
Thank you.
Adam

Answer 1

Q1: OOTB No: not directly.  If you configure requried fields for a document folder, the problem is, the file gets uploaded first, and then the user is prompted to configure metadata - if the user clicks Cancel at this point, the file is already uploaded
but without the required fields configured.  Additionally, the file will be "Checked Out" and not visible to anyone yet, because no previous version exists to display.  On the other hand, you can create a drop point where a file is initially
uploaded, and then have a workflow check the file: if it has the appropriate fields completed, the workflow copies the file to the appropriate folder.
Q2: kind of: you can configure default values for required fields, and when the user is prompted to configure metadata for the file (now already uploaded at this point), the default values will prepopulate the metadata fields and the user need only click
Save.  On the other hand, you can create a workflow that configures these fields for you, after a new file is added to the library.
Q3: yes: use document libraries.  think of document libraries as a convenient security container: all documents entered into the library inherit the security configuration of the library.  Best practice is not to use document libraries to recreate
the folder structure you see physcally on your computer or network by implementing folders within a document library.  Rather, separate out documents by the security that they should have and push these into a document folder.  Then, if there is
further grouping that you want to do for these documents, us the convenient grouping, filter and view tools available for each library to create the grouping and views onto the library that your users need.  By keeping the library simple in this way,
you realize several key benefits.  1. Users can quickly sort and find documents based upon metadata: if documents are further grouped using subfolders, this will not work, and users must click more things to get to the documents they actually want. 2. By
keeping the actual document structure in the library linear (ie, no using subfolders), you can create views that enable one-click access to key document sets of interest to your users.  3.  By using linear organization (ie, no subfolders), you can
implement analytics on the library, by configuring column counts and other features; and you can much more easily implement more sophsiticated analytics using PowerShell.
Q4: no. There are no rules as to the number of document libraries
at a site. Rather, the number and type of such libraries should match your business needs and logicall organization of your documents. There are however, best practices and technical thresholds to be mindful of when considering the the
number of documents to have in each library. There are performance considerations to keep in mind and there are technical thresholds regarding the ability of views and quieries on libraries dependent
on the number of items in the library.  Check out 
Plan document libraries in SharePoint 2013 and
Software boundaries and limits for SharePoint 2013 for additional details. 
Q5: see links above.
Q6: yes.  Doing so requires that you "disinherit" the library permissions from the parent site.  this is easy and straightforward, but does add an additional management task to permissions management for the site. For eaxmple, a site
having five document libraries all haveing unique permissions now has six permissions management administration tasks that need to be looked after: one for the site and one each for the document libraries.
Q7: Yes, so long as it is in the same web application - security and user groups are application at the web application level - sites and objects in a different web applicatin will be configured under different security groups.  Now, if these sites
are in different web applications or even different farms, but are in the same AD domain, not a problem: just ensure that the same AD user groups are used for both.  otherwise, you will need to work with your NOC to have trust relationships and so on
setup.
Q8: yes: the new item event is triggered.  Workflows can be triggered OOTB on new and modified events.