I’m sorry he is being such a shit person and father, I can see you are angry and frustrated with him. I know it’s very hurtful he treats your child so badly.
However I don’t know the answer to your questions - you need to ask your OWN solicitor not his.
What do you do if your DD doesn’t want to go with her uncle at pick up? What would the court consider is reasonable for you to do ? Are you to persuade her / threaten her / force her ? Or just let him do it ?
What should you do if you think that uncle is aggressive with her ?
What should you do if you are running late - traffic and public transport problems are sometimes unavoidable ?
what do you do if she is sick ?
should you use the app even if he doesn't t ? i assume the point of it is to be able to prove that you told him information eg “ DD won’t be coming today as she is off school with a tummy bug “. Then if his brother turns up and you don’t , it’s not your problem.
Id not leave notes in the school bag as there’s no proof that you sent them.
I understand that you are upset that he’s with his affair partner now, but as you know that’s not relevant to your daughters right to have contact with him. Although I can see that could make her less likely to want to go, if AP is there and she doesn’t like her.
Sadly there are many dads who treat their kids like shit in an attempt to get back at their ex. Mine is the same although fortunately my kids are teens so they are not forced to have contact with him - it’s their choice ( and they mostly choose not to see him ).