Is it possible to play this game without a walkthrough or I am setting myself for failure?
I'm quite puzzled by some answers you've received.
The game is extensive, but mostly straightforward. You may need walkthrough to obtain the best possible outcomes and for some advice on tactics.
Other than that, you don't need it. If you wish to be thorough, then you won't have any problems with, say, 90% of the content this game provides. And the best possible results that I mentioned above, I think, are meant to be challenging to obtain in the first place.
You will probably want to play with walkthrough, though, If this game captivates you. I think it does require some emotional investment, so why the hell shoud anyone settle for something less than perfect? I'm pretty sure every single person in this thread who enjoyed it and played it to the end is a bit of a min-maxer, ha-ha (not to mention that
Fulminato, who gave you one of the answers, is actually the person who made the lives of us all easier with his output).