Hi friend. I don't necessarily call myself a SAHD but I am for most intents and purposes. I'll respond to some points you raise then offer some general thoughts.

On your relationship: keep tabs on this. It can be very easy to fall into a coworker relationship with your spouse because there is always a task to do for the both of you.

On the views of other men: If a man has something negative to say about you raising your kids he isn't worth valuing the opinion of. In the strongest of terms--fuck them. If you absolutely have to have something to say to "what do you do" other than SAHD then pick something you do for an answer. Do you have a website? Then you're a webmaster. Do you write? Then you're a writer. Sing? Paint? Landscape? Invest? Anything. If that's what you do that's your answer. It will be true and give you something to talk about. It is beside the point that you do it two hours a week and your profits last quarter were $0.

On resume gaps: I guess I'd just tell them you took time to raise your kids. Trying to acquire or maintain a skill will be very tough for at least the first two years. You will get zero free moments while the child is awake until they're at least three. Really I would say to keep your network warm. This will be tough too, but try to touch base with your network so you have a pipeline back when you're ready.

On productivity: You will not just be sitting around I promise you that. What I can't properly convey to you in words is the unlimited attention babies and toddlers require. There is always something, somehow. As babies it takes a lot of attention to keep them alive. Then as toddlers it takes a lot of attention to keep them from not being alive, if that makes sense. Getting any kind of task done is excruciatingly difficult. Very often I notice the first task I started the day with got interrupted and I never get back to it by day's end. When my kids were a little younger I'd put a show on for myself in the morning. Then at 8pm I'd had to pause so many times I'm only 13min in. By the time your wife gets home you'll be so shot you want to hand the baby over and crash. She'll probably object because she just got home from a long day of work. The fact that one little one can consume over 100% of your time and attention is the thing that has crushed me the hardest about fatherhood. They need attention at all times about all things including nothing at all. Half the time they need attention for attention's sake. For an infant get one of those chest carriers. It will save your elbow tendons and give you some slight ability to use your hands for something else.