As for today there are two valid restrictions: One is due to the Treaty of Non-Proliferation of Nuclear Weapons. Therefore Germany renounces the development and use of nuclear weapons. The other concerns the upper limit of military manpower. In the reunification treaties with the USA, UK, France and Russia Germany accepts an upper limit of 370.000 personnel. Germany renounced the development and use of nuclear, biological and chemical weapons in these treaties as well. Other than that there are no unusual restrictions I am aware of. Everything in that sense, such as limits on submarine development etc. have been lifted a long time ago. Since the US and the other allied powers have relinquished all occupational rights concerning Germany in 1990, no further restrictions exist. There are certainly no limitations on numbers of aircraft, size of warships and such things. If we want, we could begin constructing an aircraft carrier tomorrow (at least we would be free to do so)
It should be noted though, that most of the former restrictions were in effect for some time because of the will of the Soviet Union and, partly, the german people itself. If it would have been for the US, Germany would have regained more military rights much sooner since it was a valuable ally during the Cold War. For example the US encouraged Germany to send troops to the Korean War and later to Vietnam. The same happened with the French in Algeria. However none of that ocurred because of the german attitude towards its military itself.