Hello and welcome.
If you read through the thread on your machine, there is all the info there, plus lots more, spread over many pages. The stock baskets seems to be very good quality, I presume you are using the single floor basket and fresh beans?
You should be able to adjust the dose down on the grinder to get the right amount. You want the tamped level to be the depth of the metal cap on the standard tamper. There are great guides by breville on youtube which will probably answer/confirm what you are doing is ok.
The plastic thing in the handle is purely to isolate the pour hitting the metal of the PF that may not have been pre heated. Most people remove it and the current machines do not have it.
Naked PF will highlight any deficiencies in your pour, and I always use one now as I find its also easier to clean up (no coffee residue on the bottom of the PF).
The pour time sounds about right maybe a touch short, but if it tastes good to you that is the main thing. Is that where you are stopping the shot manually when it starts to blond?
Also, check your OPV setting in case yours is set too high (some of them were), its an easy adjustment by a service centre. You should be getting no more than ~9bar even if the machine is choked.