I am also a teacher. I went back ft in June when ds was 6 months old, and then went to 4 days a week in September. I left teaching in July as I was lucky enough that my husband (also a teacher) got promotion and I was able to leave. I still do supply one day a week to keep my hand in (and my sanity).
I,like you, dreaded going back to work, especially as ds was so little, but it was fine. Last year he was in nursery 4 days a week and he caught every bug going. He seemed to have a permanent ear infection for about 6 months. I took a lot of time off, as did my husband and we both got a 'talking to' at work.
I would see if you can do 4 days a week max. It was a bit difficult to manage, timetabling-wise (I'm an English teacher so see the kids practically every day), but they managed it. It was lovely to have a day a week with the little one, but still have adult conversation on the other days.
The other hard thing to juggle is the bloody marking, which really ate into my weekends, and having to work every night once ds had gone to bed.
The holidays are ace tho!