I could have sworn you could only roll over an HSA ONE time in a lifetime (according to IRS rules). Correct me if I'm wrong here.
you may be thinking of an IRA to HSA rollover
HSA to HSA rollover is limited to once every 12 months
Also, Is it possible to contribute to my HSA with already taxed money? As in, contribute to my HSA with dollars that were already taxed from my paycheck and then claim them on my tax return?
you can certainly put after-tax dollars in (although that reduces some of the HSA attractiveness), I don't know the tax implications though