."" A maintenance company can be Subpart G and F approved, which means that the
same person may manage your aircraft's airworthiness and also do the work on it when required. Most companies I know want to keep the whole operation in house as they do now."
Not so! the
organisation can manage continuing airworthiness, and the same
organisation can do the servicing & maintenance. But the
person doing the servicing is not allowed to carry out management & review of continuing airworthiness. No time to dive into my copy of part M and the relevant MA... but airworthiness review staff in an organisation have to be separate from the servicing and maintenance people.
You could have a maintenance organisation that has the minimum of just two people, one does the dirty work and the other does the paperwork.
Edited to say the relevant MA is AMC MA 707 in NPA No 2007-08 and as it has been translated from the original French it is bl***y hard going!