Ok the items I can give are these: magmarizer electrizer reaper cloth protector upgrade dubious disc oval stone kings rock deepsea tooth/scale light ball lucky egg rare candies stick thick bone master balls net balls safari balls cherish balls also all of the plates and items that boost a certain type of move razor claw razor fang white flute black flute blue flute yellow flute red flute dusk stone dawn stone sun stone leaf stone water stone fire stone thunder stone and all of those other items I don't really use
Not on this set, no, it isn't. Hmm... Perish Song isn't a great move in general because even the AI will switch out. Lapras is alright at using it, I suppose, since it isn't amazing at anything. Yes, Destiny Bond is a very good move. Froslass is an excellent user of it.
Three spreads will suffice. 104 HP / 252 Atk / 156 Spe, Adamant. 16 HP / 252 Atk / 240 Spe, Adamant. 72 HP / 252 Atk / 4 Def / 180 Spe, Jolly. I would use the first personally as it helps out with your bulk, but any of them are fine depending on your playstyle.
I don't think they should "replace" characters, they should just add to them. Keep the veterans from the very first game. I think that my own signature is probly the smart way to go with finding a successor to Lucario and Pokemon Trainer, cause Gengar, Gallade and Gabite are all just as awesome!