This awk can do all this in one command:
awk '{if (d) d=d RS $0; else d=$0}
/>/{s++;next}
s==1 && /[ACGT]/{gsub(/[^ACGT]+/, ""); n+=length($0)}
END{print s, n, "1" RS d}' file
2 441 1
>Sample_NameA
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
>Sample_NameB
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT
ACGTGTCTAGTATGCATGCATAGCTACGACTACGACTAGCATCAGCATCGACTAGCATCGACT