My situation is a little different since my comic is much more closely related to Korean webcomics than Japanese manga. Your question could easily be converted to accommodate the differences, though.
The comic:
http://tapastic.com/series/keol
I'm using the vertical scroll format, which is the norm for Korean webcomics; in addition, more than half of its dialogues are officially in Korean (although I upload an English version on Tapastic, a good portion of it HAS been written in Korean and are even better read in Korean in some cases).
Right to left? No. (note that Korean webcomics are not read right to left, either; they read left to right, just like English)
Vertical scroll? Yes
Korean SFX? Not in the English version.
I never really liked reading SFX translations in the gutter, personally.