I disagree with you on who the great multitud dressed in white is on the 6th seal. To me, It is clearly the church... Not to mention the fact that this great multitud is the first time John actually see's a great multitud in heaven during his vision...
To the church of Sardis
He that overcometh, the same shall be clothed in WHITE RAIMENT...
To the church of Philadelphia
Him that overcometh will I make a pillar in the temple of my God, and HE SHALL GO NO MORE OUT:...
That pretty much means that we (the church) will serve Jesus (the lamb) day and night in His temple!
As much as you want to quote Rev 1:6 by stating that we are priests and kings, that doesn't matter in this case, we still serve and will serve the King of kings and Lord of lords - Jesus Christ.
As far as what Revelation 7:14 says, in original King James Version (not to be confused with NKJV) it says these are the ones who came out of "great tribulation" and not "the great tribulation", these are two very different concepts when you add the "the" to the statement. This is just the way i see it...
Regardless of how in the end this pans out,
To Christ be all the glory!