True, but I think that the point that Petrichor was trying to make was that anyone can build muscle, not that it isn't easier or harder for certain people.
Agreed. Another good reason for beginners to train 3 times per week (I personally like starting beginners on 3 total body workouts per week) is because it gives them a lot of practice at the lifts. Remember that lifting weights has a skill component and the more you practice the skill, the quicker you will get better at it. It is also crucial that you acquire the correct biomechanics for the lifts to prevent injury in the future when you are lifting appreciable poundages.
I'd also agree with this advice.
Also, to second Petrichor's advice above, you need to EAT, EAT, and then EAT some more! Ectomorphs (which I would consider myself) need to eat a lot of food to put on muscle. The sooner you realize that it's probably going to be diet that is your true challenge, the better off you'll be.
Here is a calculator for you to figure out how many calories you need to eat each day:
Next, do a log (record) of all the food that you eat in a week. I know this can be a little time consuming and a pain in the ass at first, but it'll be a great help in both showing you how much you actually eat and in the future to track your caloric intake.
There are several sites online where you can then find out the calorie content of the foods that you eat/ate. Here is the one that I happen to have bookmarked, if anyone else feels they have a better one, please don't hesitate to post it.
Most ecto's ("hardgainers" as they often refer to themselves) think that they eat a ton of food. Yet, when they actually do a food log and figure out how much they actually eat, they're often surprised to find out that they aren't eating nearly enough to gain weight/build muscle.
My advice is to stop worrying about what is the optimal number of times to hit the gym, or what are the "best" exercises for "hardgainers" and instead just worry about lifting progressively heavier poundages on all of your lifts, eating enough food to allow for growth (sticking to your diet at least 90% of the time), and getting enough rest (whether or not you are able to progress in either weight, or number of reps with the same weight by the next workout should tell you if you're getting enough rest).
Hope this helps.