hi Emily sorry for the delay....that is actually a tricky question, i did see many having the same issue....i would include it with the relationship but at the beginning cuz it's more important....if u put it separate u will see that some things might overlap (u would start to have questions like: is this more for the relationship or more for common-law? like the support letters - they can b included in both but u shouldn't put 2 copies of the same thing and also u would want to keep them together; or travelling same thing - important for both, and so on; u can make a toc and main sections like supporting letters, cohabitation proofs, joint assets, finance, memberships (all the joint things), travelling, communication, etc....then under each one u will put a short description of the actual proof....this way is inspired from Love_Young organization and TOC, do search for it
same if u put it with the sponsor or the sponsored part, it's hard to decide which to include where....
i think if u have that common-law paper signed then u can put that together with the additional documents for the sponsored person, in ghe group where u need to show civil status docs....it really depends on how much u have too, u don't want to make the sponsor or sponsored package too bulky....anyway wherever u put it just reference it well and refer to those proofs in the questions from the forms
if u apply for common-law then the table is more important cuz they need to clearly see how ur relationship developed and since when u lived together and where (some people might live together continously but in different places/countries)
as for ur other question abt the address: it's ok to put Canadian mailing and/or residential address even if ur visa office is berlin...it is actually a normal frequent way and it's ur right to apply through berlin based on ur nationality
we r in similar situation (mailing/residential address in one part of the world, visa office in other part based on the nationality)....good luck!!