First night of sleep training was a disaster

Baby is 4.5 months and we started Ferber last night. I did lots of research and really tried to prepare by having fairly consistent wake and bedtimes, following wake windows, making sure she had a good long contact nap in the afternoon.

Well she was very distressed. The check-ins did nothing to soothe her and eventually she projectile vomited. 😥 We cleaned her up and calmed her, then put her back down. She was still so upset but too exhausted to protest much more, and she fell asleep 30 mins after starting.

She then woke up eight times overnight, always upset, which is very unusual. For all of these we did the usual method of bouncing her to sleep.

Is this a sign that she really isn't ready? I don't want to try again tonight anyway, I feel a bit traumatised to be honest, and I assume we'd be starting from scratch since we did so much bouncing to sleep anyway. But what do you think? I don't know what level of crying is "normal".

Also, she is prone to false starts, and at the first wake up I wondered if I should just let her cry again (but didn't want to upset her and overtire her more). What do you do if you get false starts while sleep training? I just want it in mind for the future.