While to many bodybuilders, the idea of eating a lot of potatoes (for muscle growth) may sound like utter nonsense, I can attest to its efficacy because when I was eating about 9-11 potatoes a day and doing even moderate bodybuilding, my muscles seemed to be growing MORE than when I was eating around 35% animal protein.
I am still even a little in shock, even though it's my own body I still have a hard time believing it...lol...but on McD, muscle building is not at all an issue (at least not for me).
Interesting. How much carb calories do you consume a day?
Here is the interesting thing, I am not even very interested in getting big, muscle wise. I've been trying to put more emphasis in getting lean, not muscular but my muscles keep growing nicely.
To answer your question, I was eating around 2,300 calories a day total, 80% as carbs. Mostly from potatoes, yams, rice and bananas. Eating that way has been far more effective than when I used to buy protein supplements and eat eggs and meat ALL day long. I still can't believe it because it almost seems to defy science, but, it's true.
The last couple of weeks, I've dropped to just 1,600 calories because I am more focused on reaching single digit body fat levels (i'm close) so I have not been doing much muscle building work and have been doing more cardio to use my time more efficiently for my goals of leaning out more.
The other interesting thing is that I was only doing 4 sets per body part with exercise bands and not even barbells and I'm still getting good results so I almost suspect that letting my muscles rest more is working better than constant lifting (not sure yet, but all the evidence seems to point to that).
I will probably put up a video of my results some weeks down the road when I get to my desired body fat level.
You shouldn't have any problems. Since you want to purely gain weight and muscle, I might aim for above 2,800 calories (total, not just carbs), probably even a little more.