Hey there, we did this cycle route in summer 2018. We were staying in Vienna. We took the train to Melk, rented bikes, biked to Krems and turned in the bikes. We did not find a lot of wineries or eateries along the bike path that were open. We didn't see any that were directly on the path; we cycled off the path into little villages a few times and what we found was closed. I don't remember what day of the week it was, but we set out from Vienna fairly early and reached Krems in the late afternoon. It's possible we were too early in the day. Anyway, we did finally come upon Campingplatz Rozsatz, across the river from Durnstein. We were starving at that point. We stopped at the visitor's center, which had a very casual restaurant with basic outdoor patio and sold camping supplies, propane, etc. With my rudimentary German I managed to understand that the restaurant was getting ready to close for the afternoon and if we wanted anything, we'd better hurry up and order. I ordered two schnitzels and two glasses of house Gruner Veltliner. Ten minutes later two sizzling schnitzels the size of trash can lids with pommes and two glasses of excellent wine were set down in front of us. It was the best meal we had in Austria.
We didn't do any research on what might be open before we set out. I would recommend looking at your route on Google Maps and seeing what's there, then checking their hours.
Do be sure to bring plenty of water with you. There was no place to buy any along the way. When we got to Krems, we stopped at a grocery store to buy some, but it was already closed (at 6 pm). Now that I'm remembering this, it must have been a Saturday. In Austria they roll up the sidewalks on Saturday afternoon and don't roll them back out until Monday morning. We stopped at train station grocery store when we got back to Vienna and it was absolutely mobbed, because nothing was going to be open on Sunday.
It's a lovely ride. Lots of grapevines, and pear and apricot trees in bloom along the way.