Ans1: If you want to train his speed and sp attk then buy 10 of those those vitamins and feed it up. Out of 252, 100 evs will be given to it. So you will need to train it for the other 152 evs!
Ans2: You have not mentioned which game you are currently playing.
Fire Red:[ FRLG EV training spots(wild) ]
<< HP >>
Three island port through cave(after national Pokedex) Dunsparce(1 HP EV)
Ruin Valley Water LG only Marill(2 HP EVs)
Ruin Valley Water FR only Wooper(1 HP EV)
Route 6, 22, 23, 25 Water LG only Slowpoke(1 HP EV)
Viridian City Water LG only Slowpoke(1 HP EV)
Fuchsia City LG only Slowpoke(1 HP EV)
Four Island LG only Marill(2 HP EVs) Slowpoke(1 HP EV)
<< Attack >>
Mt. Moon B1 Paras(1 Attack EV)
<< Defense >>
Route 21 grass Tangela(1 Defense EV)
<< Speed >>
Diglett's Cave Diglett(1 Speed EV) Dugtrio(2 Speed EVs)
Route1 Pidgey(1 Speed EV) Rattata(1 Speed EV)
Altering Cave Zubat(1 Speed EV)
<< Special Attack >>
Pokemon tower Gastly(1 SA EV) Haunter(2 SA EVs) run from Cubone
Route 6, 22, 23, 25 Water FR only Psyduck(1 SA EV)
Mt. Ember B3 Slugma(1 SA EV)
Viridian City Water FR only Psyduck(1 SA EV)
Fuchsia City FR only Psyduck(1 SA EV)
Unknown Dungeon FR only Psyduck(1 SA EV) Golduck(2 SA EVs)
<< Special Defense >>
Kindle Road Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Treasure Beach Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Bond Bridge Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Outcast Island Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Green Path Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Water Path Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Trainer Tower Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Tanoby Ruins Water Tentacool(1 SD EV) Tentacruel(2 SD EVs) Mantine(2 SD EVs)
Route 4 ,10, 11, 12, 13, 19, 20, 21, 24 Water Tentacool(1 SD EV)
Pallet Town Water Tentacool(1 SD EV)
Cerulean City Water Tentacool(1 SD EV)
Cinnabar Island Water Tentacool(1 SD EV)
One Island Water Tentacool(1 SD EV) Tentacruel(2 SD EVs)
Ruby/Sapphire/Emerald
Pokemon that are recomended you should battle for your EV points are listed.
Sapphire/Ruby/Emerald
- Whismur ( hp) - cave on route 116
- carvanha ( attack) - route 119 in the water with the super rod
- sandshrew/Skarmory ( defense - a little difficult because of spinda but the only easier way) - route 113
- spinda ( special attack much easier to find than sandshrew/skarmory) - route 113
- tentocool ( special defense) - almost anywhere you can surf
- zubat ( speed) - cave of origin
Ans3: Yes you should start right away!