First off, great Alternate History idea, and good luck with it!
It was the Austrian Empire not Austrian-Hungarian Empire during the Crimean war. The United Principalities did not occur to 1859, so Moldova and Wallachia were separate nations. Here is quasi-decent map from an older thread:
https://www.alternatehistory.com/discussion/showthread.php?t=114863
Austria had a historical interest in the Danube Provinces, so she might get drawn in if she gets to keep them. She occupied them during the war OTL. With that said the 1848 revolts were bad (ethnically, economically, & militarily) for Austria, and Austria did owe Russia for helping her out in 1848 (OTL she did not repay Russia though). However, OTL was the worst outcome possible for Austria. She did not honor Russia who had helped her, and she did not join the Allies in attacking Russia. This left her completely isolated diplomatically after the war. This benefited both Sardinia (later Italy) and Prussia who were able to beat Austria in later wars thanks to her lack of allies (plus Austria's own military weaknesses).
Also until late 1857 Radetzky is still alive potentially able to lead troops, so Austria would have an experience and very capable general. He got sick in late 1857, and died in January 1858.
Long-term Austria with the Danube provinces is a very different situation (she would be an oil giant in the early 1900s with Galicia and Romanian oil). Also, the ability to play the Hungarian and Romanian people off each other (There populations would be roughly equal, both would want Siebenburgen, and both are not Slavic) could definitely aid the Germans in keeping effective control of Austria. Austria also would not be as isolated diplomatically post Crimean War, and would have a more experienced military (hopefully better generals too, Ferenc Gyulay was a moron). Though, France being allies with Sardinia in trying to form Italy probably would happen no matter what, as it was definitely in France's best interest to push Austria out of Italy.