As far as HSA goes, I've only got one kettle so when I am spargeing I run off into buckets and then add the sparge water. I put my kettle on the burner, pour in the first runnings and start heating and run off the second runnings into the bucket which is again poured into the kettle. I've not noticed an issue so far but that is just one anecdotal experience so take it as it is.I have the same sparge routine. Last time I participated in a club brew day, all the old guys freaked the heck out when they saw me doing it.
HSA was a boogeyman when I started brewing. Unless you are making very light lagers and looking for a year shelf life, one should not get too concerned. Charlie Bamforth says there are many other things that we should worry about and get control of before we worry about HSA.