Thank you! I will generally post on weekends, not weekdays, but this was a special case.
The 4 day combine is still intense, but there are more activities (including psychological and medical examinations, and additional tests they don't include in the one day combines) and also more participants (~100 players for the 4-day combine, while there is ~100 players spread across the 3 one-day combines in Melbourne, Adelaide, and Perth).
As for Liam and Neil, they explained things in a conversation with Ollie and Helena back in chapter 4. If they moved in together and then they broke up, Neil would be left stranded. Liam could move back in with his parents, but Neil wouldn't have a place to stay. Also, Liam wants Neil to concentrate on his studies -- he doesn't want him to work parttime while he's at university.