NBN... National Broadband Network (AUS)
FTTC... Fiber to the Curb.. ridiculous..
NCD... Network Connection Device
TPG... ???

So to get my MT working with this new NBN it was a bit of a headache.
So posting this for reference and someone else can avoid the same headache.

First off... TPG is the ISP of topic.

So they say you can use your own router to connect
to the NBN. They give you the option to either purchase their modem/router (TP Link) combo
or use your own. Since I was an existing customer I was charged an additional $10 for the provided
TP Link modem/router. I accepted it as a backup in case for some reason I could not get my MT working.

What they do NOT tell you over the phone is that they pre-configure this TP Link modem/router to actually
move your NBN connection from PENDING to ACTIVE status. During the pending status NO other router/modem
can be used to connect to the NBN via TPG. They do some sort of authorization/authentication from the provided
pre-configured TP Link modem/rotuer to activate the line. AFTER the line is no longer in the pending state and is active;
THEN and ONLY then can you use your own router. Again, they do NOT tell you this over the phone.

So after all that I did finally get my MT to connect over PPPoE with the new NBN by way of TPG...
And yes you have to set your VLAN-ID to 2 for your outward facing PPPoE connection. Then you
don't even need a password to connect; all you need is your username. So in theory I could use
my buddies TPG username and connect and I wonder if he had a faster NBN plan then mine; if I would
then get faster speeds... 1 session per connection of course....

This is more a TPG thing then a NBN or even Mikrotik thing - so the post probably has little relevance here - might be a good post for the Australian Whirlpool forums or something.

In particular though, your question of whether or not using your buddies username would give you more speed - the answer is no. The speed profile is set by NBN on the physical connection, so if he buys 50/20, and you buy 25/5, using his username on your connection would still only get you 25/5. On the flip side, in an odd twist of fate, depending on how TPG set up their network, using your 25/5 username on his 50/20 connection (these are example numbers mind you), could actually limit down to 25/5. There's a very long answer on why this iis, and is RSP dependant but just thought I'd chuck that in there hehe.

Source: I run a wholesale aggregation network in Australia for NBN and xDSL services.

Excellent, thanks for that response.