My first (and current) game was Poland. Ended up in a two-front war - invaded Crimea, then the Ottomans, joined a scruffle with Sweden. Managed to force a peace - then got DoW'd by Courland and Denmark. In the meantime, Portugal got annihilated by Spain, which in turn got kicked out of Italy by Venice. France and Austria beat each others head in, so I swept into Central Europe, taking Prussia and Austria down.

One thing I think is that the likelihood of other nations DoW'ing you depends on the pace of your territorial acquisition. I expended so far and so fast, nearly every state in Europe is diplomatically hostile to me. I wasn't in the mood to tempt fate, so I bribed them off with state gifts to pacify them but I get the feeling that if you go on an all-out land grab early on, others start to see you as a threat and that increases the chances of random DoWs by anyone in the vicinity - i.e Courland and Denmark.