1) yes there is, but I couldn't tell you where to find it, so here is where I EV train in DIAMOND(not in Platinum, Pearl works)
HP: solacean town, bike down and right before the bike ramp there's a cowgirl with 5 Bidoof. 1 each + PKRS and power item= 10 each, so you're getting 50 EVs per fight
ATK: go to your hometown and use the SUPER ROD on the lake below you. there will always be either Gyarados or Seaking. both of which give you 2 EVs +PKRS+Power Item=12 EVs per fight
DEF: go to the Ruin Maniac Cave. there are only geodude and Hippopotas there, both giving 1 DEF EV. 1+PKRS+Power Item=10 EVs per fight
SPATK: go to the Old Chatuea(spl?) and battle the ghastly there. if you don't have a GBA game in then you're guaranteed to run into ghastly every battle. they each give 1+PKRS+Power Item=10 EVs per fight
SPDEF: This one's anoyying, but go to Pastoria City and surf on the lake on the bottom right. you have a good chance of running into Tentacool(1+PKRS+Power Item=10 EVs per fight) and a rare chance of meeting a Tentacruel(2+PKRS+Power Item=12 EVs per fight). You also have a chance of running into wingull and Pelliper. Wingull gives SPEED and Pelliper give DEF EVs, so you want to run from them
SPEED: Fly to Eterna City and bike to your left. there should be a group of four fishermen, 3 of which will battle you. you want to battle the middle one(facing to your right) and he has 6 Magikarp. 1+PKRS+Power Item=10x6=60 EVs per battle
2) I have no clue :/
3) Reaper Cloth
4) there are not many STAB users, but the move Ice Beam is on several pokemon, so you'll need to watch out