By about a year of age they are past the more fragile stage of life and are suitable for life outside 24/7/365. They can be placed earlier and I have done it but there is an increased risk if they are put in at a few months of age and go straight into winter - as mentioned above they won't have sufficient fat reserves. If it's the other way round and they go into the pit at 6 months of age and we are going into summer giving them another 4-6 months of warm weather things will be fine.
I would suggest not having "wire all the way around" as they then become too exposed to the elements. Depending on what outdoor enclosure design you choose I would suggest have at least two sides with a weather proof material (plywood, corflute, colarbond) to provide some protection from cold wind and rain then at the opposite end extreme heat in summer.
The location of the cage should NOT be in an area with as much sun as possible. All you want is morning sun, any more then that and on the first 35c + day your lizards will die without some underground bunker to shelter in.
Oh and poisoned insects is such a low risk I wouldn't even allow it to enter my thoughts when planning an outdoor enclosure. Also seeing that the central coast area of NSW is home to a massive population of eastern blue tongues there is no issue at all with RI providing they are not kept in a swamp. I keep blotched blue tongues outside with no ill effects.