We try and test with all the various hardware and software versions from Apple.. it gets harder and harder to do this as the older hardware gets depricated by Apple, and new iOS functionality will not work on these older devices.
In terms of iOS versions, we expect you to upgrade to the latest supported version for your device. We can't regression test new versions against every release Apple has issued in the past!
I find the latest release of SQRemote on the devices that support true multi-tasking to be great - responsive, fast and really works for my setup.
I would say that spending the time to get the best and optimal home wifi network is well worth while. I recently moved house, and spent the cash to try the latest Comcast ultra-high speed internet (I was getting 70Mbit download wiht a wired connection) - only to find that my Apple Extreme was down grading the through put to 1Mbit on my iPad when I sat on the sofa.... Ahhh time to survey the house, work out optimal place to put routers etc.
Home control doesn't need the throughput, but it does like a quick connection and low latency. Checking what channels your neighbour's are using and finding the least busy are good things to do. I am going to try out all our test routers/access points (we have A LOT) in my new home to see which is actually better too.