From what you stated, you just opened 4 new accounts in the past 30-60 days? If your score doesn't drop 25-30 points, I would be surprised.
Ditto on the drop, though I think most will return by the time you refi.
And you don't need to use them monthly. They will still report monthly regardless of use and FICO will score accordingly. Just use them every 3-4 months at a minimum to avoid closure due to non-use.
They will still report monthly regardless of use
Are you sure? My experience is that no use of a card in a given month doesn't update the account's Date of last activity field in a credit report.
Of my 20 or so CCs, all of them update monthly despite months of non-use. Admittedly I haven't studied the DOLA field in that relation, but a new "OK" appears each month so the TL is updating.