2 a days are a great way to build size. I did them last summer and it was pretty effective, although I would say total body training 3x a week is more of what you're looking for if you are trying to gain strength more than size.
And yes - 2 a day full body workouts are possible, that is exactly what I did. I did two muscle groups a day, with around 3x8-10 on approx 4 exercises per muscle group. I trained on mondays, tuesdays, thursdays, and fridays. I must admit - having wednesday off seemed to be key for recovery, I wouldn't do 5 days straight if I were you. Also, never work them out any less than 5hrs apart.
Also note - I never trained the same two muscle groups more than one day in a given week. this isn't necessarily the best way to do it, but with high volume like this it allowed me to not overtrain
Just as a means of reference, the actor (Jane Thomas I believe) that played the Punisher used a very similar program and jacked up incredibly quickly. Good luck.