Hi Luigi,
We have not heard much from Fly for some time. Maybe I can help.
Climate: E. camaldulensis grows over much of Australia - from arid (almost desert) areas along rivers to cooler foothill country. summer temps to well above 45C through to winter min around -7C so these are pretty tough plants. I am not sure what the min temp would be for bonsai in a pot because there are few areas in Aust that get cold enough to freeze the pots.
They do like some moisture and are mostly found along rivers and can tolerate flooding for several months but will grow better with well drained soil as most bonsai.
You can expect some leaf size reduction in a pot but the best euc bonsai I have seen (even small leaved species) are larger trees about 1m tall. Euc as bonsai is new and some growers are experimenting with different techniques to find what works.
Thread grafting should work but very little work has been done with grafting eucs. Grafted trees have only been available in nurseries for about 5-10 years.
I think euc is better outside. I do not think anyone here would try keeping one inside because we have no reason. Again, you will be trying something new and results would be valuable for the Australian plants as Bonsai research team.
As far as styling goes red gum comes in all shapes and sizes but most aussies would think of a massive trunk dividing into several ascending branches with weeping tips (a bit like the 3rd pic here). For inspiration some pics of natural red gums:
Copy of Red gum beechworth.JPG
Copy of Red gum leaning Beechworth.JPG
Copy of Redgum bowna 1.JPG
Copy of Red gum - Meringo 1.JPG
Copy of Red gum Meringo 2.JPG
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