[biocit]

Ok, I take number 2 back. Learning English through katakana would definitely mess up your speech, but I'm not talking about that. There's no real difference to using "Ga" over ”が”。　English is a flexible enough language that different sounds can be defined differently whilst using the same letters. Not knowing how to say, "Onegai Shimasu" using romaji is not the fault of romanized letters, but it's the lack of knowledge in Japanese speech and pronunciation. Just by knowing kana does not give you a Japanese accent.