I would much prefer to watch the entire series in one go. It is perfectly fine with me if that happens 5 years from now.I'd recommend watching the first 2 seasons. At the end of season 2 they wrap up a lot of things. There's obviously a lot of story to come, but there are no cliff hangers at that point.
Since you haven't read the books, you won't be bothered by the changes. Nevertheless, they squeeze a whole lot of stuff into those 2 seasons. So if you know someone who has read the books, don't be afraid to "call a friend>" Or you could just ask here.
By the time you finish the first 2 season, it may be time to plunge in to season 3. As of today, there are only 3 episodes left in season 3.
No point in waiting until the "final season." Nobody knows if/when that will be. It seems clear that we'll get at least 2 more seasons and fans are hoping for many more.
I definitely do not lack shows that I've been meaning to watch. What I lack is the time to watch them all.