Question. If Little Serperior had just gotten infected with Pokerus, and held a power item, how many EVs would he obtain with them alone? (Disregard which power item he is holding, but know it isn't a macho brace.)

Tick, tock, tick, tock...

The Power Items (Aside from the Macho Brace, which is often assumed to be the same sort of thing, hence why you specified) add 4 EVs to their respective stat regardless of which Pokemon is defeated. Pokerus stacks with this and doubles it. Thus, the Pokemon would gain 8 EVs from just Pokerus and the Power Item.

(Technically it would also gain EVs from the Pokemon itself, though. (Ex.If your Pokemon KOs a Machamp while wearing the Power Bracer and infected with Pokerus, it would gain 8 EVs from the Power Bracer's effect being doubled by Pokerus, and 6 from the Machamp's EV Yield being doubled by Pokerus, thus yielding 14 EVs in total.))

You sir, earned yourself an A+

(Thanks for that. I always seem to forget the whole EV training basics. Welp, time to ev train Little Serperior.)

Edit: wait... Machamp yeilds 6 Evs? I thought it was only 3 EVs...

You guys are so smart... I congratulate you. You guys have passed this pop quiz.

(meanwhile, my head is spinning with all this basic algebra that I should be knowing, yet I still keep forgetting...)

Edit: My final question.

Given that a pokemon's total evs are 508. How many pokemon should Little Serpeiror defeat in order to plug in his evs for the following stats:

HP: 108
Atk: 0
Def: 100
SpAtk:100
SpDef: 100
Speed: 100

(note, I think i know this answer, but I need clarificaton.)

I'd do it this way:

Assuming you have Pokérus -
Hold a Power Anklet and defeat 8 Basculin at Route 3 for 96 EVs, then take off the Anklet and defeat one more for 100 Speed EVs (Found by surfing)

Hold a Power Lens and defeat 10 Litwick at the Celestial Tower for 100 Sp. Atk EVs

Hold a Power Band and defeat 10 Frillish at Route 4 for 100 Sp. Def EVs (Found by surfing)

Hold a Power Weight and defeat 9 Stunfisk at Route 8 for 108 HP EVs (Found by surfing)

Hold a Power Belt and defeat enough Pokémon at Pinwheel Forest to get 100 Def EVs (Sewaddle, Venipede (1 EV each) and Swadloon, Whirlipede (2 EVs each))

Thanks guys for your help. You all get the honor roll.

Time to EV train.