As long as your friend knows what he/she is doing and isn't a danger to your group, then sure. But solo is the best way to survive/play because the only person you can blame for your failures is yourself.

Yes it is. Having just one other person besides yourself brings tons of logistical benefits that lighten the load. You can have portals placed for you remotely instead of having to plan ahead for every last one of them. You can multiply how many boats of cargo can be moved at once. You can employ distraction tactics in combat so that the other player may more easily capitalise on opportunities for bonus damage.

I did my first playthrough solo but so much time gets sank into thoughtless toil. And of course when you are solo it is a shame to pour so much effort into building a structure that nobody else will get to appreciate.

I would strongly recommend playing with another player if for nothing but the more flowing pace.

If you like Minecraft and Don't Starve I think you'll get along quite well in this game. You can solo it too if your friend doesn't happen to be on, but you will have to be careful especially when entering a new biome. Each biome is a different difficulty level.

My wife and I play together all the time. We are occasionally joined by another friend.

YUP 2 players is more than enough I have a good friend I play this with and we really enjoy the dynamic.. one of us like to build.. the other likes to farm.. we take turns going out to different areas and gathering stuff then all the hard content we do together. I honestly think 2-3 players on a team is the perfect amount as long as everyone is like minded in what they want from the game.

Absolutely.

I play mostly solo and it's amazing.