Having more players doesn't change anything. More mobs don't spawn and bosses have no more hit points or attack strength in multiplayer than in single player which makes taking them out in multiplayer easier.
Starred wolves only spawn at night. They tend to come in packs with other wolves. They spawn at the places where the day time wolves spawn and you can attract their attention by making noise. 2 star wolves only have a 1% chance of spawning so if you kill wolves and let them respawn you have a better chance of rolling that 1%. The downside to that is that by the time a 2 star wolf shows up it may be very close to morning and you might not get a chance to start taming before it despawns.

Go ahead and tame 0 and one star wolves as you find them that way you can start breeding them and only have to find one 2 star wolf to start breeding and culling your pack to all 2 stars.

I've always had more trouble finding a 2 star boar since the tame ones won't follow you and you can't really transport them to where you want them. The 2 star boars I've found have always been on the border of the meadows and the plains and most of the time fulings or deathsquitos kill them before I can get them back to my base.