Ds2 is year 12 so this is how it went for him. A level predicted grades are based on his GCSEs (mean value) this can be useless if they have a spiky profile ie 9s in the subjects they love and are taking at A level but 5s in MFL or science. Ds1's mate was predicted Bs based on that but he got As. Predicted grades don't mean much at the start, just crack on with the work.
Regular end of topic tests in year 12 confirm if they are on target. Ds2 has already had 2 reports, November and February. He is sitting pre-exams this week and next week to cement exam technique. He has the week before May half term as study leave plus May half term. His end of year 12 exams are the week they go back in June.
This summer, Ds is booked in to 2 paid for summer schools, they are online and 3 days each. He has also been selected by one of the Big 4 to also do their summer program. He is predicted 4 A stars and will have basically half of July and August off. There is plenty of time for holidays.
So not that intense, however, because his brother has been through the whole uni process he knew to start doing extra bits early so he can document things on his personal statement. Ds uses his free periods (5 hours worth even with 4 A levels) to get work done, his friendship group are a high achieving group so all focused on work, then gaming and chatting in the evenings as all their work is done.
July/end of year 12 uni applications are mainly focused on those going for early entry. But Ds1 had summer school stuff to add to his but they wanted them to at least start it and submit something as he was early entry. Normal deadline is mid January. Sometimes it is worth waiting until after year 13 mocks to get a more accurate grade prediction. Your year 13 thoughts are pretty accurate.
GCSEs to A levels are a bit of a jump but also not depending on the work ethic of the child and a willingness to succeed.
Re uni, if they know what they want to study go now, there are open days in July when they will have finished GCSEs. Accommodation is a long way off, some unis wait until after exam results to get students to pick, some after the May deadline for all offers to be out and a smaller number make you choose early and some students decide not to apply to these because it pressurises them sometimes withdraw their outstanding UCAS applications to other unis so they can firm their choice and choose the accommodation there. It is completely shit and I think shouldn't happen.
But I think what you are doing, looking ahead etc is important. Look at uni courses now, see the entry grades which are the minimum they take people in on, see if there are any specific subjects for A level too.
Year 11 summer is 10 weeks ish, they can use that time to explore their subjects a bit, absolute wealth of information online on A level topics. Both mine had summer work set by sixth form but it was fairly easy to get through considering how many weeks off they had.