Yes it would be fine, but a better translation of "i am eating my breakfast" would be "saya sedang makan sarapan saya". "sedang" in indonesian means "currently" if it's used to explain time, and means "medium" to explain level as in low-medium-high. Sorry my english isn't that good, tried my best to explain it!
For past tense "i ate my breakfast" you would want to add "sudah", as it means "already". "saya sudah makan sarapan saya" can mean both "i already ate my breakfast" (or is it "i ate my breakfast already"?) and "i ate my breakfast", since in indonesian we don't have a past present and future form of words/verb.