Sí, hize los cambios (de pretérito perfecto a simple perfecto) a causa de concordancia verbal; sin embargo tus frases iniciales eran buenas.

Comprendo* (son las cinco de la noche) quería decir, creo que comprendO) jaja

Jajaa creo que comprendes más o menos lo que dices, aunque es tarde y he de traducirlo bien para asegurarme. Realmente creo que me hablas de la falta de concordancia verbal, me gusta mucho que te molestes y cuenta conmigo también para cualquier explicación o duda que te surja, Saludos y mil gracias.

I hope I didn't confuse you!! In my first correction, I changed your present-perfect sentences to simple perfect sentences. In my comment above, I tried to keep your present-perfect sentences as they were in the original entry and clean them up a little bit.

I can relate to your wanting to practice different grammatical tenses, like the present perfect, very much, because I always want to do the same thing in Spanish. But for many of the sentences in your first paragraph, the present perfect is inappropriate. For the sentences in the first paragraph, I would use the simple present tense instead of a compound present tense. But, if you must use the present perfect, I would write: I have woken up late because I didn't sleep well. Secondly, I have had a breakfast of milk and muffins. Finally, I have already walked the dog. I have done all of this while my brother sleeps. (I hope that I understood what you meant to say and that I preserved the meaning of your sentences there.)