Well I'm sure you're not starving him! If he eats every 12 days consistently, I'm sure he's fine. Wouldn't be any different than a snake refusing a meal one week & taking one the next. Until yesterday, 2 of my snakes were going on 2.5 MONTHS of not eating. Sometimes they're just stubborn. But yeah, every 5 days for babies & then every 7 days for larger sub-adults/adults is good. Give it a try!
A scale is one of the necessities, I'd say. Though it's not MAJOR. I like having one handy for those weeks/months they decide to not eat so I can keep an eye on their weight and make sure they're not losing much, if any. Are you keeping a record of when he eats/sheds/poops (& how much he weighs when you get a scale)? I find this helpful as well. It might not be too hard to remember if you only have one lil guy, but when you have a collection, it's much easier to have something concrete to look at when you're curious about when they shed last or when they pooped last.
I found that soaking the rats directly in water was something my snakes didn't like. Maybe it was because they lost their smell or maybe because they were just wet, but they wouldn't eat them. I used a blowdryer on them one day and sure enough, they took it, the little buggers (though, it could have just as easily meant that they weren't hot enough). If yours takes it wet, awesome! You're lucky haha.