Your late to the "wedding" Largoras but welcome aboard.
Yes you can make great Song of Ice and Fire armies out of Fireforge and Perry. Here's a rough guide:
Fireforge for the North (add some fur cloaks from GW) with leaders in more advanced plate (HYW). Midlands (Tully, Frey, Aryn Perry HYW (only plastic foot so far so you have to used metal for mounted).
Perry War of the Roses for South (Knights of Summer).
Leaders of course could wear heavier armor (they can buy it from different sources) but this is a good guide for rank and file.
Northstar (Frostgrave) barbarians make great Wildlings (though rather pricey). Some of the latter Bretonians make OK Night Watch.
Martin has recently confirmed in a Time interview that the books are based on the HYW and War of the Roses as to setting and politics. So any figures for those eras will work well (the North subject to the full brunt of Winter has stayed a bit more feudal).
The direct tie in game from CMON isn't due till 2018, figures are oversized 32mm so won't work with other lines. Nice sculpts based on books – pricey though. Rules have many board game like features and only vaguely resemble medieval battles. Still seem better than current Warhammer and do use mass bases like Kings of War (but with figure removal thank goodness).
But for now build an army Perry/Forge work great. Bring it to DragonCon, Siege of Augusta, NashCon or Historicon and compete for the Iron Throne (we have Knights and Knaves, Fire and Ice editions competitions at all these cons).
Thomnas J. Thomas
Fame and Glory Games