In regards to the question of playing solo characters: you need very good stat raising gear that increases the stats you'd otherwise be weaker in with your character build. From what I understand, you don't need higher than level 2 in any stat to activate all available conversation or observation options, such as finding required information and hidden objects or alternatives to the linear narrative. I'd avoid playing solo until after level ten though, it's a bit tough in places before that, but that's obviously up to you.
And no, no time limits... yet... other than otherwise specified