The little balls are slow release fertilizer prills. The insects are the larvae of one of the many scarab type of beetles, we call the larvae 'grubs' here. Many grub species are root chewers.

It looks like those roots were a little root bound --- outgrew their pot, but look pretty healthy to me. If you have heavy clay, then the hole you dig for plants will act like a pot --- the roots will grow in the nice soil you have in the hole and not expand beyond it.

Japanese beetles will munch all sorts of plants and can overrun a garden, but otherwise, grubs are just normal. Part of gardening is figuring out what works for you. There are so many variables --- sun/shade, heat/cold, acid/alkaline soil, sandy/clay soil, etc, etc,

See what your neighbors grown and if they have success where you fail, ask them.

Of course, there is the most obvious question --- do they get enough water? It may seem like a no brainer, but if you moved from a place that had heavy, slow-draining clay to sandy, fast-draining sand, it might take a while to realize that your new garden needs a lot more water than you were used to giving your old garden. (And vice versa).

Many of the plants you buy can be root bound and that may be your problem. When a plant is root bound the roots start to go round and round at the bottom. If planted that way they continue to go round and round. The plant can't get nutrients and suffers and can die. No matter how healthy it looks on top it's the roots that matter Always look at the roots when you take it out of a container. If they are going around the bottom loosen them so they are hanging straight down. Don't worry if some break, you are doing the plant a favor and new roots will soon come..

I once told this to someone who said she couldn't grow marigolds. I guess she almost tore the roots apart but she ended up with beautiful marigolds. You don't have to be that drastic but do loosen the roots

It should be pointed out that there are thousands of different species of scarabs in the world, most of which start out as white grubs. Some are true pests, others not so much. If I were to find "an abundance" of grubs in my troubled garden areas, I'd be very suspicious.

By the way, I don't believe Japanese beetles exist in Australia, but I'd be willing to bet that it's populated by plenty of other scarabs.