: Is it on sale? This sentence is fine. :Do you guys have soy milk? Yes, we do. This is also fine, very natural. :I usually start working at(from?) 3:00pm. "I usually start work at 3pm" or "I usually work from 3pm until 10pm." Only use "from" if you will say when the end will be. :Can I switch rice to noodle? (When we order food at a restaurant) This would be fine to say but it would be better to say "Could I have noodles instead of rice?" :Who inspired you to study Japanese? This sentence is fine. ^_^

Just refer to a group of people or an entity as "you". "You all/you guys" is is not proper English but can be used in a friendly conversation. English is odd because it does not have the structure of other languages so you just have to become comfortable with its differences.