> once we have the branch merged is there a way that we can mark this as a release?
As a release of 'mobile services', yes

>Is a tag sufficient on the repo.
yes

> We want to show that this is a 0.1.0 release of sync and the accompanying docs should also be identifiable somehow.
that's the tricky part, we don't publish from the code repos, all docs are in one repo, so how do we label it, all docs labelled with tag as being related to sync 0.1.0? I'd suggest a simple attribute data-sync-version and add it to 'in dev' note from above.

>Once we complete another sprint we aim to do another release e.g. 0.2.0 until we believe there is enough functionality to warrant a major 1.0.0 release. Did you have any suggestions in mind in terms of docs on this front.

update data-sync-version to 0.2.0, then 1.0.0 and remove the 'in dev' note suggested in comment above... everything else is 1.0.0, so nothing else required, make a splash on aerogear.org if you want to 'announce' it.

> Taking into account this would be separate to the overall release of Mobile Services.
as above, that's the tricky part... The prevailing attitude seems to be that versioning/compatibility is a problem that we don't need to tackle right now.