You can also find chocolate syrup. Add that to milk, no chocolate milk problem solved.
Late to the party, but in Nagahama it's very normal to be placed in just one elementary school - you may even have another ALT in the school with you if it's big enough. I think there were at least 10 ALTs when I was there who were at one ES, and a few more who switched schools every couple days but were still exclusively ES.
At my ES I wore khakis or other slacks, polo shirts, light blouses/fancy t-shirts, sometimes a dress or skirt that went to the knees. I'd recommend pants more than skirts, since you'll be doing a lot of moving around. The other ALT at my school wore dark jeans sometimes and that was fine. There was another ES ALT in the area who wore cut-off jean shorts, that was not fine. I think capris and a polo would be perfect. And your black slacks and black blazer should be good as a suit - I can only remember having to wear a suit maybe 2-3 times a year.
I wear dark pants and a t-shirt (sometimes a blouse) at my elementary schools with normal flats. I'm probably considered 'overdressed' since everyone wears track suits or capris with crocs.
I'd just make sure that your shirt doesn't fall open and show anything when you bend over.
Everyone keeps mentioning t-shirts, but do these t-shirts have graphics on them or are they blank t-shirts? And what kind of pants are your dark pants? Jeans? Slacks?
How low can your neckline be without being inappropriate. I'm used to wearing unisex t-shirts with absolutely no neckline, so everything I've been trying on see seems very low cut to me.
I wear a t-shirt that says do not arrest this person
Most T-shirts that teachers end up wearing are various sports brands - le Coq Sportif was all the rage in the staff room the last two years. Before that it was Puma and Adidas. Most "dark pants" are pretty much anything other than jeans - but usually fairly casual slacks ranging from "sporty" (think hiking pants) to baggy sweatpants. One (male) teacher I work with wears tights under athletic shorts and a windbreaker everyday - even when it gets north of 30 C. Then again he's about 40 kg soaking wet and a long distance runner.
Shirts should show no cleavage and no shoulder - the "support teachers" tend to wear polos with both buttons done up or more rarely with the top button open. Dress code at the school for students also specifies only collar button should ever be undone. (That's JHS level though - they might have a dress code for students that you're broadly supposed to follow as a teacher as well.) Short sleeves - even the very short, as long as it's below the shoulder - seem fine in my schools, but that might hold for all schools.
emcee of a tourist luau
Both. But not, like, band t-shirts or your souvenir shirt from Disney World or something. Sports brands are probably okay because sports are king here. I usually wear shirts with subtle designs so I can also wear them at JHS but another girl I know wears brighter colors/designs to get the kids' attention.
Uh, I guess they're slacks? They're not jeans or dress pants, although I can wear jeans as long as they're black. Gray or navy pants are fine as well. Basically anything that's not blue jeans.
If you bend over and you can see everything down there then it's too low. It doesn't have to be a turtle neck, but it can't show any cleavage. If the neck line goes below the collar bone then I'd wear something under it like a camisole or tank top.