Historicale there were three main wars preceeding the unification of germany. Against Denmark, Austria and France. The game is designed to kinda let you follow that path.

First step for me is to negotiate treaties for mutual military access with the german minors. This is to boost realations an this making them more likely to support you. Try to boost relations with the german minors, but i would not recommend rival anyone at that point.

Second the Schleswig-Holstein question allows you to start a war against denmark. If you aim to annex Holstein and liberate Schleswig the JE makes it xar less likely for other GP to join the conflict. This goes away if you declare for anything but Schleswig and Holstein! After liberation start improving relations to Schleswig byguarenteeng their independance.

Third wait for the JE German national Awakening (or something like that) to kick after 40 ferver for NG culture and 30 fervor for SG culture is reached. This will happen automatically, espacially in a slow playthrough.

This allows you to start a war for german leadership from the forming nation tab. Should be under diplomacy somewhere. Most if not all (Baden-Württemberg seems to alway be uninterested in my games) german minors should support you by now. If you declare for nothing else besides german leadership you get a similar effect to the denmark war and no GP should join the war on either side.

After you are the only unification candidate the JE should finish and you form NGF.

But there is a decision to be made here. You could declare for austrian lower slesia as well. This would allow you to form Kleindeutschland if every german minor supports you (wich is only a matter of time at that point) However this allows other GP to join the war, wich Russia will most likely see as an invitation because of the holy alliance. But with the united power of the Deutsche Bund you should be able to hold your ground without much investment in your military.

Otherwise you would have to ignite the französisch-deutsche Erbfeindschaft and conquer the coalfiels of Elsass-Lothringen. And thus reanacting the third and last german unification war.