Well, i'm scared of huntsmans, but rarely actually see them. NSW has the funnel web, i think everywhere has red-backs, but i've only ever seen two red-backs and only a couple white-tails, too. As for crocs? i've never seen an actual, live crocodile. but i think im really in the wrong state, and like has already been said, they're mainly in NT. As WA is so big, there are several different climates, but unfortunately there ARE meant to be more sharks in WA's coast, although still not many and it is still quite rare to have a random encounter with one. if you choose where you go carefully enough, you should be able to get the perfect spot for yourself!
For the whole wheather business. well, its not all hot all the time. everywhere has a winter!

Tassy is generally coldest, then Vic, NSW, SA?, QLD, and then WA and NT. QLD is really hunmid and stormy in a lot of area's, NT is REALLY hot, Vic and Tassy are too cold, in my opinion (still lovely in summer, though), SA... i don't know much about it. and WA is just huge, i think the more southern part and generally around Perth is sort of hot but average? not sure... but i've been there loads and i love it (especially Rockingham and Rottnest Island

) seriously, WA's winter is Vic's spring. literally! another thing for the whole shark thing, once you get in the water, you're generally having too much fun to think about them and so you forget. The water looks too inviting when you first get there, and when i go to the beach for the first time in ages, i always absoloutely, full on SPRINT into the water (unless its a rocky beach).
i hope this helps a bit!