Not being an English dub person, I'm not so interested in that stuff (though I obviously hope FUNi does it right, and I'm sure they will). For me, I like the Japanese versions of the songs. Hayashibara Megumi singing the [b]Slayers Next[b] OP theme "Give A Reason" is awesome (IMO). It is my favorite of the Slayers themes. That said, FUNi doing the English for ANY of the songs depends on licensing.
FUNimation seems fairly clever about merchandise, so they could do some stuff. I can see them possibly going in with TokyoPop on the novels (though it is a shame that TP didn't do them right). BUT with an anime title as old as Slayers is, will audiences be as hyped to get this kind of merchandise?
As for me, I'm just looking forward to FUNimation's superior subtitles and I hope they do the 4-disc release per series.