MrsB - the rule of thumb here is that if it makes a "proper" web, it's far less dangerous.
Huntsman and white tail spiders don't make webs, they're active hunters, which is why they run so fast.
Redbacks make a messy sort of web in cracks and crevices - seeing a mess of leaf bits and stuff in outdoor toys etc. is usually a dead giveaway that a redback is lurking behind it.
Funnelwebs - well they make the traditional funnel shaped web but I still haven't seen one of those around our place, although we've seen a couple of the spiders themselves, one in DH's bath towel
- only a small one and it ran away under the washing machine.
Stolemy - that's really interesting that your DS got the necrosis, because there is still a lot of resistance to the idea that white tail bites cause necrosis, despite anecdotal evidence. If you read up about it on the net (never a good idea!) the "authorities" claim that there is no real evidence that white tail bites cause necrosis, but you are not the first person I have heard from who has experienced it first hand, so I don't know where the difference of "opinion" comes from! Still best to avoid them, IMO!
I don't kill Huntsmen, I leave them to themselves, but chuck them out if they come below the picture rail (and I can catch them).
Redbacks get stamped on, hosed and stamped on, hit with shoes or whatever on sight.
White tails - I've only caught one and I ended up leaving it under a glass for a day while I decided whether to let it go or kill it - ended up killing it with a sand bag.
Funnel web - only seen the one, as I said, couldn't do anything once it went under the washing machine.
DH (the Aussie!) got a bit confused about the black house spider webs that were in the house after it had been empty for a year before we moved in - thought they were funnel webs (they do look a bit similar) and killed all the black house spiders with spray. That was a bit upsetting. I still won't kill a spider that is no threat to me.