Re: Virgin taxi speeds, not sure for the 73, but the E-jet used to have quite restrictive taxi speed limitations, which recently became recommendations. (Wet turning - 5 knots)
However the nose wheel on the 170 is prone to skidding during a turn on wet painted bitumen and concrete. Check out the deck angle next time, and it'll make sense.
As for not tucking into the holding point I have no explanations, I personally pull up with the hold lines in the corner of the L1 flight-deck window. Probably 1-2 metres short of the lines.
Cheers,
Leatherdog.
blessings on the blue skys