Thank you, Ven. Appicchato, for your kind advice to the monk-to-be.
I believe it would be best for the monk-to-be to travel to Thailand and visit a few monasteries and see for himself where he is welcome and where he will find friendly monk-brothers who will help him tie his robe and tell him what to do and what not to do.
Maybe it would be good advice not to travel to Thailand during the Rains Retreat (vassa) from 2 AUG to 30 OCT 2014 as most monasteries will be full and busy. After the Rains Retreat the monasteries will return to normal and resident monks will have more time to talk to visitors.
Once the monk-to-be has found a wat where he feels welcome, visa problems can be sorted out. To start with an invitation letter seems risky to me because the monk-to-be may be stuck with a monastery and a teacher where he doesn't feel at ease.
There are more than three thousand wats in Thailand. Trying to find the best wat in Thailand is like trying to find the best taxi in Bangkok. The official place to start for foreign monk candidates is Section 5 of Wat Mahathat in Bangkok. But why start in Bangkok? Why not in Hatyai?
Monks in South Thailand generally welcome foreign Buddhists and are relaxed and helpful. Phra Kroo Aphicharto at Wat Bo Pradoo (T. Watjant, A. Sathingphra, J. Songkhla) is a modern young teacher and head of a small monastery. He is very kind and speaks English well. He is a good ordination guide. In the area there are several monasteries with serious, intelligent young monks.
The Fourfold Path: Proposed to everybody, imposed on nobody.