As another said, structure is already good. The words are correct in a strict grammar and vocabulary sense. However, just as there was different way to say one thing in Korean, it could be awkward to use your sentences in a normal conversation. 'Aku' is more usual in a friendly conversation than 'Saya', much like '저' and '제' And a more informal way to say those words would be these: 1. Aku takut kucing. 2. Aku gugup sekali/banget. 3. Aku gembira sekali/banget. 4. Aku bosan. 5. Aku capai/capek. 'Sekali' would literally translate to 'once' or '한번' , but in informal use it means 'very' or '너무'

Struktur kalimatnya sudah sangat bagus. Kosakatanya juga sudah benar. Untuk percakakapan informal, "capai" biasanya diucapkan dengan kata "capek". The structure of the sentences are already very good. The vocabularies are also correct. For informal conversation, the word "capai" is usually pronounced as "capek".