Questions 2 and 3 are the same thing WRT effect on your credit score, because it will generate an inquiry on your report. The inquiry will have a small negative impact - a few points, in most cases. Whether you are approved or denied won't matter - it's the application for credit (the inquiry) that affects the score. Additional inquiries generally have a smaller impact. Inquiries count against your score for 6 months, and stay on your report for 2 years. Some issuers will decline new applications if they see a large number of inquiries, others don't care.
Question 1 might or might not matter to your score. Some CC issuers will increase your limit without pulling your credit report again, and in that case, there won't be any inquiry. Some will do a "soft pull" which does generate an inquiry. Some will do a "hard pull" which DOES generate an inquiry.