Osaka was my stomping grounds for a while. I loved it.
Most of the gay life is in kita, near the Hankyu railway station, as is most of the Osaka nightlife.
Yuji owns the most gaijin-friendly bar in town, BarButch
http://www.barbutch.com/. You'll be very popular there.
You'll meet enough people there who will take you from bar to bar. Many people are very friendly but very shy, so don't be afraid to make the first move. Plus there'll be enough gaijins there to fill you in.
As in most gay bars in Japan, the places are tiny but intimate. Fine-tune your best rendition of "Moon River"