i would then stay and instruct
You need a visa for that and the J1 visa is no longer issued.
you dont need to take a selection test to see if you pass and get accepted.
You don't need a selection test for many schools in the UK either; only if you want to go on an integrated course.
getting training down there isn't considered top notch
I've always held the training in South Africa in high regard.
Cheers
Whirls