Out of curiosity, why are you spending 3 nights in Hittisau?
I don't think that is a good location if you want to visit Meersburg, Mainau, Reichenau, etc. You'll spend too much time driving back & forth. I was just in Meersburg this past week and go there several times a year. If I were planning this trip, I would have made Meersburg my base and visited this village along with Mainau, Überlingen, Freidrichshafen and Konstanz. Lots to do in this area. I like walking along the Bodensee (Lake Constance) from village to village.
I've, also, been to the Bregenzerwald numerous times, not in Hittisau, but Lingenau. It's a beautiful area and known for it's cheese. If you are determined to stay 3 nights in Hittisau, I would drive the Käsestrasse from Lingenau to Bezau and explore this area on one day. Another day, I would visit Bregenz and, if you have the time, Lindau. You can ride a tram up the mountain in Bregenz. I would also suggest visiting the Rappenlochschlucht near Dornbirn. This would fill your Hittisau days.