Unlike Norm, I do "specialize" in Weimar lugers- though it is a very confused and confusing time and the lugers that were used are a challenge to understand and to explain!
I believe your pistol started life as a .30 caliber "commercial" luger, the barrel was replaced and numbered to the frame.
This could have been done in a navy workshop and the Ostsee marking applied then; or before in commercial trade only.
However, since the upper was not numbered to the lower when manufactured, it may have no original relation to the lower frame at all, and could have been assembled at a later date from a Navy marked lower frame and "an" upper of commercial origin. The Barrel was likely numbered when the barrel was changed or when the upper was mated to the O marked lower.
The Ostsee number of 1354 would have been added about 1934- at a time when the Reichsmarine(Weimar) Navy was building up and would soon become the Kreigsmarine(nazi) Navy.
So, either the pistol was in Navy hands before that date, and numbered to the Ostsee as a complete pistol, or was assembled later(postwar) from a collection of parts.
Long story, but the bottom line is that it is not possible to know when, where, or who assembled your luger in its current configuration.
Because of the unknown heritage, I would say it is an "interesting" shooter- due to the Ostee markings.
Value is whatever you or someone is willing to pay for an "interesting" luger.
JMHO.