Re: Activation a local purchased sim for online promotion
The $2 sim card will work fine for being able to join Boost and you can then recharge the $200/100GB plan via the phone app. While you will be able to recharge using any of the standard plan offerings, you won't get any additional promo price/bonus though (sometimes there is promo for cheaper if you buy a preloaded sim pack etc).
And yes you can now bring your number across from Telstra the usual way. No need to do anything special anymore.
* I am a Boost Australia customer. This is a peer to peer community where users help each other.