The answer to #3 and #4 is that you should put the package in hold status once you've installed your version. This tells the Debian package management system to "hold" any future changes to this package, in effect lets you manage the package manually.
From the Debian FAQ:
7.11 What is meant by unknown, install, remove, purge and hold in the package status?
These "want" flags tell what the user wanted to do with a package (as indicated either by the user's actions in the "Select" section of dselect, or by the user's direct invocations of dpkg).
Their meanings are:
unknown - the user has never indicated whether he wants the package>
install - the user wants the package installed or upgraded
remove - the user wants the package removed, but does not want to remove any existing configuration files.
purge - the user wants the package to be removed completely, including its >configuration files.
hold - the user wants this package not to be processed, i.e., he wants to keep the >current version with the current status whatever that is.
7.12 How do I put a package on hold?
There are three ways of holding back packages, with dpkg, aptitude or with dselect.
With dpkg, you have to export the list of package selections, with:
dpkg --get-selections * > selections.txt
Then edit the resulting file selections.txt, change the line containing the package you wish to hold, e.g. libc6, from this:
Save the file, and reload it into dpkg database with:
dpkg --set-selections < selections.txt
With aptitude, you can hold a package using
aptitude hold package_name
and remove the hold with
aptitude unhold package_name
With dselect, you have to enter the [S]elect screen, find the package you wish to hold in >its present state, and press the
=' key (or H'). The changes will go live immediately >after you exit the [S]elect screen.
Note: People have found issues with the aptitude hold command, so imho you should prefer the dpkg command to hold the package. Alternatively, you could hold the package via the Synaptic package manager GUI interface (Package > Lock Version). My preference is to use dpkg because it has worked well for me.
You already have a good answer for the rest so I'll not venture my opinion on those.