The website of the Heilbronner Hütte has a pretty nifty leaflet concerning the tour you are planning. It is in German but I guess you'll be able to read the graph.
Be aware that it states:
Diese großartige und abwechslungsreiche aber sehr lange Tour wird nur
ausdauernden Berggehern empfohlen.
which roughly translates to "This amazing and varied, yet very long tour is recommended for experienced and persevering mountain hikers only". The terrain and trails seem to be "easy to medium".
I have made the experience that warnings of this kind issued by the alpine club should usually be considered a fact - which does not mean you shouldn't do it in case you are in reasonable shape, but if you aren't, maybe look for something around 4 to 5 hours, it's no fun hiking for 10 hours if you're already exhausted after 4 of them.
Also be aware that if you are going in early summer (June & July) the chance of thunderstorms is very high in the afternoon / early evening, so if the weather report is not 100% sure, you better leave really early so you're at the hut you'll be staying overnight at something around 4 or 5 P.M., maybe even earlier. You really don't want to live through a thunderstorm at 2500m.
In case you want to buy maps I can recommend either the maps issued by the German alpine club which are really detailed (you'll need those if you want to leave the trails) but rather expensive or the maps made by the biggest commercial map maker Kompass from Austria, that make rather cheap but still very useful maps, many of them come with an accompanying booklet that has example tours and hut infos.
In general, I would always recommend the huts' websites as the best resource for planning tours in the alps. 99% of them have one and they put a lot of effort in keeping them up to date with useful information. Google Translate will be your friend in case you don't speak German. There's an interactive map at the website of the DAV that will guide you to every hut in the eastern alps.
Have a nice trip and enjoy the alps!