He was ordained after St. John reposed, however, he was baptized by St. John and also received a blessing to form the brotherhood that later became the St. Herman of Alaska monastery in Platina, California.
The article on Orthodox Wiki is accurate and provides a complete picture of his life:
Seraphim (Rose) - OrthodoxWiki
And here on Google Photos you can see the numerous icons written depicting him: icon of fr seraphim rose
His cult of veneration is quite large and includes myself. By the way, have you read
Orthodoxy and the Religion of the Future, or
The Soul After Death, or his book on the dangers of Nihilism, or his translation of
Orthodox Dogmatic Theology by Protopresbyter Michael Pomazansky?
I find it surprising that someone as traditionalist as you is not more familiar with his work, since he was a protege of St. John Maximovitch. I strongly reccommend his work
Orthodoxy and the Religion of the Future, which has proven to be prophetic.
His most vocal opponent is the extremely controversial liberal retired ex-schismatic Archbishop Lazar Puhalo, who falsely believes the doctrine of tollhouses to be Gnostic, and who also had to be ordered by Metropolitan Tikhon to stop making pro-LGBTQ statements.