My little boy started last week. He's just going one day a week. I had such mum guilt! He cried when I dropped him off so I had a cry to my partner on the phone. He loved it though and I got updated throughout the day x
Mine has gone for 3 settling in sessions over the last two weeks. In terms of feeling overwhelmed I would recommend writing a list of questions you might have for the nursery and if you are invited to go for a stay & play session ask them then. The nursery my little one goes to we were asked to fill in an About Me questionnaire to put our preferences for things like naps, food and milk. After doing that I felt much better. So far we have had 2 really good sessions and one where my little one got a bit grizzly but they messaged me to ask about current teething and then messaged again when she was feeling better.
It's ok mum feels that way and emotional about it but I'm sure it will be fine and it's a big step for your little one and for you. I'm not planning on doing it just yet.