The topic was well covered in an earlier thread on marrow a couple or three months ago.
The classic bordelaise is made with sauce espagnole to which is added shallots which were first sweated in butter, then cooked in wine until the wine reduced by 2/3, some herbs, some marrow lightly poached in salt water, and enough brown stock to create good consistency. The total volume of espagnole should equal or be slightly more than the total volume of reduced wine and the stock, and be twice as great as the volume of marrow. Thus, for 1 cup of espagnole, you'd start with 3/4 cup of wine and reduce it to 1/4; and use 1/2 to 3/4 cup stock, and about 1/2 cup of marrow. Sometimes a little lemon juice is added as well.
1. The marrow may be chopped fine after poaching so it will dissolve and enrich the sauce, it may be left in large chunks, or the techniques may be combined. If the techniques are to be combined or the marrow left in large chunks, you'll have to do something to provide structure that otherwise would have come from the marrow. You can use a butter finish, reduce the stock slightly, or simply use more marrow.
2. I prefer to reserve the shallots, herbs and marrow until the liquids have been combined and sieved for gloss and consistency; add the lemon juice off heat; add the shallots and marrow; sauce the meat; then add the parsley after the meat is sauced.
3. If you're not starting with espagnole, then make whatever it is you consider to be bordelaise -- either from stock or demi-glace -- and add marrow in something like the proportions I suggested, and herbs, acid and aromatics in the proportions you prefer. Other than using tinny canned stock or radically over-salting, this is so good it's hard to do anything to screw it up.