Sharks may also bite you by accident, because they mistake you for a seal.
How dangerous a bull is also depends on his age. While getting older he will start to lose the fear/respect for humans. This will get to a point where being alone with him is a literal death sentence.
It should work with both ways. First time I did them with archinstall(but didn’t like that it created a separate partition for my home directory). Second time I manually partitioned my drive and then let archintstall use that.
Archintstall sometimes produces problems(at least I had problems with it). Make sure that you have the current iso version of arch on your stick and try again.