"I drink alot of water and read that they do not serve tap water at meals." They usually will if you ask. Expect to pay €1-2. Various carbonated beverages are usually available as well (frisdrank). I particularly like Tönissteiner on a hot day when I don't want alcohol.
"What types of table wine will I find here that are inexpensive, like 3-4 euro a glass?" Most good Belgian restaurants will have a larger wine list than beer selection.
"what types of vendor stall foods will I come across for snacks/meals?" Most frituurs also sell various types of deep-fried "mystery meats", as well as croquettes, which are sort of like a breaded, deep-fried stick of mashed potatoes. Besides mayonnaise, you can also get various other sauces. In the Netherlands, they have a delicious peanut satay sauce for fries. You'll also see sandwich shops ("broodjes" = sandwich), kebabs, pizza, etc. Many Dutch cities have stalls selling various seafood products, like smoked herring and eel ("harring en paling") and other deep-fried fish. During the holidays and various other festivals throughout the year, vendors sell "olieballen" (oil balls), which is the Dutch variant of a doughnut.
"Do all restrooms require coin to use?" Usually only public restrooms, although some restaurants in very touristy areas will have an attendant to collect your money.