Caloric surplus

I don't want to start a discussion about pros and cons of gaining weight (obviously in form of muscle mass) while training F1, neither about if F1 could actually put some size on someone's frame, because these topics have already been discussed a lot.

What I would like to know from you guys is how you approach your "lean mass phase" (aka bulk). How much of a caloric surplus do you aim for? Have you got a (rough) idea of how much weight do you want to gain per month?

Despite not being my main goal, I'd like to put a little muscle on my skinny and tall frame

I'm 6'1'' tall & I weigh ~79 kg. I consume ~3,500 calories a day. My diet is stable, no variations. H1 & F1 are bringing slow but useful muscle mass gains

If im remembering correctly my old research from Dr. Casey Butt says that a pound of muscle requires 500 extra calories, no matter who you are. I think he also said a pound of fat is also equal to 500 calories.

I eat three meals a day.  When I am bulking I just eat four.  All of my meals are mostly vegetables with some meat, and fruit to snack.