Whether you buy the game on steam, Kagura's website, or DLsite, every spot has its own percentage of the take. If you're looking to show support for English versions, use Kagura's website or steam. If you're looking to simply financially support Inusuku, the largest cut would actually be none of these. Inusuku actually has a system for just 'financially' supporting on their blog:
You must be registered to see the links
. Their blog is entirely free to read, but there are payment plans you can sign up for for those who just want to send them money.