You should try to have legumes at each meal today, just whatever would be a normal serving for you. That could be more peanuts, or some hummus, or some beans or peas, or some soy sauce. The only reason you might not want a serving at each meal is if after one serving you immediately had some kind of reaction and didn't feel you needed any more evidence to know that it's something you want to avoid.
The Italian dressing would depend on what non-whole30 ingredients are in it. If it's all compliant except for soybean oil, it would be perfect for legume reintroduction. If it's got dairy or some other non-whole30, non-legume ingredient, then you'd save it for the day you do the reintro for that ingredient, or if it's multiple non-whole30 ingredients from different groups, then you'd wait til you're done reintroducing everything.
Sugar/sweeteners can be difficult to avoid. They sometimes are in things you want to use for reintroductions, and that's mostly fine, although it might be worth doing a separate day for sugar-free sweeteners like equal or sugar alcohols because they can cause digestive issues for some people. A little sugar in your peanut butter on legume reintro day is not a problem.