Hello wcoenen & Emraldfire,
thanks a lot for your answers!
If your transaction was broadcast to other nodes (which you can check by double clicking it), then it will be confirmed eventually. Even if it has no transaction fee.
When I doubleclick now, I only see "0/no confirmations" but I remember that once it said something like "sent to 18 nodes". Probably that's because I restarted my computer in the meantime. So yes, it was sent.
Thanks for that link, very helpful! But no, i don't see my transaction there. I searched for the amount of the transaction (0.001) and didn't find anything.
Also note that your wallet file is the only file that holds your money, don't lose or mess it up or all your money is gone forever.
Yes, after reading a few threads I realized that and I already have (versioned) on- and offline backups. Unfortunately no backup of before this one transaction. If I would, I could recover by simply restoring that backup. With the backups at hand, I would risk manipulating the file and just not doing any transactions inbetween.
Thanks again for your help so far. Further help would be much appreciated. I know it might sound absurd fighting that much for BTC 0.001, but first that's 5% of my fortune
and second I'm really trying to test all that stuff to gain a deeper understanding of the technic behind bitcoin.