Planting Pittosporum in pots, how to start?

Hi,

I've got 4 80cm x 36cm x 36cm troughs where I had been planning to plant 2x pittosporum silver sheens in each trough. I wanted to know where to start, I am completely new the gardening.
Some online research said I needed to
-Put some gravel/rocks or terracotta pieces on the bottom of the troughs where the holes are so that the soil does not just fall straight out. True? there are 3 holes in the trough at the moment.
-Use premium potting mix from the local nursery/bunnings. What brand should i buy? I've also read that some plants do not like some elements used in some potting mixes, how do i know which one will be alright for pittosporum? Would planting herbs(coriander, sage, thyme etc) require a different potting mix compared to planting pittosporums?
-Not to bother of mulching because it is in a pot?

How often should I fertilize? and with what? would 'Thrive' work?
Should I mix anything with the premium potting mix soil?
I had been given a couple of small bags Aqua Soil and Peat Moss for free, could I use any of these products to help them grow faster?

Thank you for reading

Oh dear... I'll answer this later and your online research is why I spend so much effort and time here

Thanks Fu Manchu,
I eagerly await your words of wisdom! I am excited to start growing