....I'm also confused
In general, 3 SIMs are not as easy to get as other brands. Easiest to get are A1 and bob (also in Post offices), and Yesss! (Hofer/Aldi). Bob you also get in Libro shops or in LIDL supermarkets. 3 is sold in 3 shops and sales points which you find in shopping malls, in Media Markets, a.s.o..
For your purposes a 3 Reload Extreme would be suitable with the added Pakete MoreMB ans MoreInternational. The options are continued automatically after 30 days if the balance is sufficient. To discontinue you'll have to call the 3 Serviceline 2 days before the end of the 30 days period.
For data it is more complicated. I do not recommend you to call with data SIM, even it is possible, but usually expensive. Super SIMs can be used as Wertkarte (Prepaid) or with a contract.
With A1, T-Mobile (expensive), Yesss you don't have any trouble. Buy-insert-set APN-surf.
Bob and 3 somehow have to be activated / registered on their website for easy administration. This is not difficult, but it's in german.
Why don't you use a VoIP account like Dialnow.com or Rynga.com and call local access numbers or trigger a callback by sending some data?
In this case you could use a bob Vielwertkarte
main_contentpage login and book a Datenpaket Wertkarte for 4€/1GB/30days.
Regarding 3 like home you must consider that, if you call an italian number while in Italy, this will be an international call. Your SIM is still in Austria......
I avoid this by calling an austrian VoIP access number from Italy and then I enter the italian number. Only this way is really roaming free.
In the SCS Shopping City Süd you'll find all major phone shops like 3, Telering, A1, T-Mobile.
In this 3 shop I got my 3 Data SIM "Reload" without a modem. In other places it was completely impossible (20€/1GB/1 year which I bought for Italy).