が leading sentence sometimes serves as an introductory remark as follows. Japanese people unconsciously use this が very often. (1)いま、お金を持っていないんですが、あとで払（はら）ってもいいですか？ As I don't have money now, can I pay it later? (2)私が坂本ですが、何かご用（よう）ですか？ I'm Sakamoto. Do you want me? Then, we often omit the latter sentence wanting a listener to read a talker's mind. (1')いま、お金を持っていないんですが。（hidden request/question)=あとで払ってもいいですか？） (2')私が坂本ですが。(hidden request/question=何かご用ですか？） This が and けど are interchangeable, 　けど is casual though. I hope this helps!

"Ga" in this sentence means "and", and it's used just to connect the sentence to the next one. The speaker doesn't usually emphasis anything. It might sound a bit softer to put "ga" after you say your name, but it depends on contexts. You can imply you're annoyed or something by saying "ga" strongly.