As for MashaAllah, you could say it. It’s also something that arab Christians and many other non Muslims say! As far as I know, nothing wrong with that! (Allah = God). If you are worried about evil eye etc tho, the correct thing to say would be “Allahumma barik”, meaning “May God bless you”.
It is reported that when Ibn `Abbas was walking between the Yemeni corner and the Black Stone, he used to say: “Allahumma qanni`ni bima razaqtani wa barik lifihi wakhluf `alayya kulla gha’ibatin bikhair.(O Allah! Let me be satisfied with what You have provided me. O Allah! Bless it for me. O Allah!They said to him: “Teach us.” He said: “Say: ‘Allahumma aj’al salataka wa rahmataka wa barakatika ‘ala sayyidil-mursalin wa imamil-muttaqin wa khatamin- nabiyyin, Muhammad ‘abdika wa Rasulika imamil-khayri (wa qa’idil- khair), wa Rasulir-Rahmah. Allahummab’athhu maqaman mahmudan yaghbituhu bihil-awwaluna wal-akhirun. . 328 62 445 366 311 438 439 191