Sam2,
Your first point is exactly on point with mine – “there are SOME shitos…” That is exactly what I said. Some poskim hold you should not answer amen in the middle of ashrei. I got this from a siddur compiled by Rav Ovadia Yosef. I do not know his source.
I do not understand why my second point was self contradictory. Please explain.
And when it comes to kedusha, according to most shittos, in Elokai Netzor, you can answer the full kedusha. It is birchos krias shema where you can only answer kadosh kadosh etc.