As to when and how to apply vitamins/feathers/shop boosts:
Start at level 1 if you can. I say this since it is now way easier to get in the effort points in right off, as it will save a lot of time to just get in those ev points included before leveling up. After you have those ev points applied- it will not matter what you battle against and you do not need to focus on exactly what to battle against that gives the specific ev points you need to boost the stat.
Pokemon gain the ev points during a battle/after the battle.
If you face off against a low level Pokemon to get an ev point applied to the stat, it will be applied after the battle since you KO'd it. If the Pokemon is at a way high level, say 50 and your Pokemon is at level 92- after the KO you won't neccessarily gain enough experiance to level up (unless your right there at the point that what ever you KO will make you level up)- you will have the ev's applied during that level's experiance obtained, thus allowing you to stack those ev's during the level up battles needed.
Say your Pokemon is at level 30, and you go battle wild level 3-4 Pokemon that give you the ev's your looking for. You KO like 15, but do not gain enough experiance to level up to 31. All of those ev's are applied during that level, stacking the ev points and those ev's raising the stat as ou go on to leveling up.
If say you want to use vitimins/feathers/boost on a Pokemon that you have leveled up without actually focusing on the Pokemon that give you the desired ev points to raise a stat, you have unintentionally given you Pokemon random ev points that will be applied anywhere/everywhere (misplacing due to not focusing on specific Pokemon that give the ev's you need in order to increase a single stat like attack)- you will not be able to use as many vitamins because you have already applied ev's, thus "shrinking" the amount you have left that can still be applied.
You get only 510 total ev's, without "controling" those ev placements, you deplete the 510 down, thus the reason why your not able to apply all 10 vitimins into one stat at level 70 verse level 1.
I hope all of that made sence.
As far as building a good Gyro- I will post again in a bit later as to a good/possible Gyro for what your wanting to do.
Edit--------------------
kk-
Adamant nature- Apllies to give top max attack stat for nature, and does not hurt the speed stat.
Moxie ability- something is KO'd- free boost in your attack.
Life Orb- has recoil, but who does not like to hit extra hard?
Move set:
Dragon Dance- boost speed and attack
Waterfall- STAB with possible flinch effect
Bounce- Stab and if your fast enough speed wise, it'll get 'dos out of harms way in many cases
Earthquake- coverage from most electric Pokemon to hit for weakness.
This build is with the intent to get the most benefit to hit the hardest. If this is not exactly what your looking for, there are afew other builds/move sets that can be set for other purposes other then pure brute force.
