1.where should I be looking for miso in my supermarket?; 2. what type of soy sauce?; 3. is sugar syrup the same thing as simple sugar (50-50 sugar...

I've found miso in the section near the "fresh sushi" selection at my local fred meyer, but also in the "health food" section with the tofu. At Safeway it was with the vegan cheeses and the store workers told me it was an item that they didn't stock. I've also found it with refrigerated supplements (acidophilus, flax seed oil, etc).
Generally I stock up when I'm at a local east asian specialty store, it keeps a really long time and it useful more often than one might suspect.
If you feel that you will never use miso in a recipe ever again buy a couple of Annie Chun's Miso Udon flavor noodle bowls and use the miso packets inside for this recipe and the noodles for a stir fry or something. Do not, however, get the dehydrated packets of miso soup, they don't work very well in recipes and taste kind of funny.

This is one of those things it doesn't hurt to ask your neighborly store worker--probably won't be placed at eye level but up high or low on the shelves unless they have a selection.

I feel your pain - at our Whole Foods - the miso is in a refrigerated section with tortillas, tofu, and other vegetarian items. Right next to the eggs.

A good health-food store that sells food will have Miso, usually in the refrigerated section.
Miso Masters is a good brand (Made in Washington State I think) It keeps 'indefinitely' in the 'frdige.

Tree of life is a good soy sauce---but pricey not for large quantities. Kikkoman is a fine brand.

Simple Sugar is just 50/50 water and sugar---not reason to buy it. Just mix, heat and put in a squeeze bottle.

Yes, Rice wine and rice vinegar are used interchangeably.

Even my small-town grocery store has an Ethnic Foods section, with Miso found in the Asian foods area within that section.

At least out here on the West Coast most of the big name supermarkets, Vons, Albersons Ralphs etc., have dedicated Asian and Hispanic sections.

Miso is more and more available in grocery stores these days. I would look wherever your local store keeps tofu -- typically miso will be stored nearby. If you have a Japanese market nearby, you are likely to find more options at a better price.

Agreed with all of Quinciferous answers

Although if you're not in a Vietnamese grocery store it might be harder to find. I was able to get some at a local big name (save on foods) grocery store, near where all of the soy-sauces and asian condiments are kept. They only had one option to pick from and I almost missed it. It wasn't packaged in a bottle or jar, but rather small plastic bag.

1. Depends completely on your supermarket; there is a miso section in the Vietnamese grocery near us and other stores nearby don't sell it. I would ask at the store!

2. I imagine that regular soy sauce/tamari would be the way to go.

3. Sugar syrup = simple syrup, but since this recipe uses only an optional splash you shouldn't have to be too careful with ratios.

4. Rice vinegar = rice wine vinegar.