Of cos, you need to purchase a proper portfolio case. No need to
be expensive type. So long can hold your artwork can le. If your
artwork has a size up to abt A2, then get a portfolio case slightly
bigger than A2 one. Bras Basah Complex is a good start to look into
that.
Preferably, mount your artwork on a piece of black mounting board.
If possible, use a consistent size for all artwork mounting. If
largest piece is abt A2, use black mounting boards thruout. Looks
more tidy when place in ya portfolio case. If you wan to be careful
not to spoil the artwork after mounting it... overlay it with a
piece of mahjong paper.
Can't help you on the interview part cos me from NAFA previously.
However, we were required to draw still life during the day of
test. Can't rem if there's interview or not... too long ago liao.

Good luck.