Hi @ITguy. Congrats to your ITA.
1) You can process these 2 even before visa lodging. NBI - just indicate that it is for Australia Visa purposes. Medical - you need to generate your HAP ID by creating My Health Declaration on your immiaccount. You will then need to present this referral letter when you go to the clinic for medical.
2) Yes, you can do this. But based on others who got their Direct Grant, it is recommended to frontload most of your docs before a case officer is assigned to you, so you get better chances of DG. Otherwise, the CO will just request for the incomplete docs, and you might need to wait for some time for the Visa grant.
3) Yes, I just used BC and MC in my case.
Hope this helps.