If you have AoW Austria is so strong it can WC before 1600.
If you don't have AoW, or want a more casual game, then there's the standard Austria play.
At the start you want to RM Hungary and Bohemia. Don't ally either though. There is an extremely likely chance that both will get your dynasty. In Bohemia's case, you then claim throne and declare war to obtain a PU over them. Hungary will have an event where they choose between keeping your dynasty or electing a pretender. If this happens you will get the claim throne CB. If either of these fails, there are post-1500 missions that just give you the CB anyway.
Your main threat is going to be France. Cutting it down early is easiest. Ally up Poland, Castile, and Denmark, and hopefully you have many countries that you can bring into a war. If you're lucky Burgundy will start a war against France too, although they could just as easily go for Liege, but in that case you can call your allies in anyway.
Diplomatic and Influence are a good pair of initial idea groups for Austria. You should spend most of your game running around releasing princes. At game start you can release Pisa, Hamburg, Corsica, and a couple of others so long as you can get into a war with them. Don't intervene in HRE wars, let them conquer each other and then bring out the Imperial Liberation wars. Expand yourself outside the HRE. Breakup France and either diploannex or take-province-releasevassal the French minors. Similarly expand down into the Balkans. Make sure you always have 7 electors.
