Hi RockJock. Welcome to Germany.
You are right: Vodafone has different plans for prepaid. The Vodafone Smartphone Special that you are mentioning is one of the most common.
Be aware that allowances are now valid in all EU countries without surcharges in case you are travelling on to another country.
To check on which plan you are, there are different options. Most local people use the Vodafone.de app for it. But to get it, can be rather tricky as Vodafone geo-restricts availability in Play Store and iStore.
Another way is on your personal account "mein Vodafone".
Another easy way is to use their 'Tarif Manager' by calling 22044 (if it's not working +49 172 22044 from abroad).
How to manage this CallYa SIM I wrote down in English some months ago in a special article on the Wiki:
http://prepaid-data-sim-card.wikia.com/wiki/Euro7
If you have an Android device, you can download their app from there too, but it sticks always to German. So only recommended, if you understand some basic German.
A €15 top-up is perfect to have this plan running for 28 days. You can do it on their website for a €0.50 fee using an internatl. credit card or by buying a voucher in Germany available all over. But better be sure that your SIM hasn't been suspended in the meantime. Most German SIM cards are switched off, if they haven't been used for 1 year or more.