Aussie summer is not homogenous. The dry heat of Melbourne/Perth is different from the muggy heat of Sydney, which means that heavier linen is a really bad idea in Sydney. Would be helpful if OP can provide details of location. Unlined/semi lined jacket will help tremendously. For a 1st timer, IMO bespoke linen is going to be hard to justify price wise. RTW with alterations will be much less challenging.