Porygon2

how many candy is the evolution supposed to be? I think he will be a nice rarity to see at a gym. If he keeps his normal typing, he should make for a pretty solid defender as well. Just depends on how strong you want yours to be? I also have two in the same IV range (one with CP 861 and the other CP 857). I only have 43 candy though so I'm hoping he will only take 50 for the evolution.

So P2 is an interesting one,
with the current stat system it's max CP is 2546, which puts it just below Venusaur

So definitely by no means a slouch but does suffer from not being easily able to get to 2500+ which is where the majority of gym defenders want to be for placement

Now from an attacking point of view, I really could not say, since Porygon (1)'s moveset has rather unique type coverage
Tackle / Zen Headbutt
+ Signal Beam / Discharge / Psybeam
which makes predicting P2's attacks rather difficult (though it keeping Tackle and ZH wouldn't be too unlikely imo)

Honestly as for swapping him to your buddy for Gen 2, well it's a good idea, if you already have a good supply of candy for what will probably be more useful Pokémon (Blissey, Espeon, Scizor, Steelix, Kingdra)- which is what I'm doing atm.
Otherwise, since you're at 50 candy I would just save it for the time being and be ready to get that Pokédex entry. :)

Live for today, Snorlax or Lapras should be your buddy.

You might get several Porygons from eggs.

What happens if the Easter event has increased Porygon spawns?

Might take a while before we get Porygon2 though, for now keep something more important as a buddy.
It definitely will be a good pokemon to have, and maybe in a couple of years we will see PorygonZ as well, but his movesets might be rather weird for a normal pokemon :D