You got the gist of it. Indulging is being tolerant, letting someone do something. Taxing, here, means taking a toll, being hard on something. So taxing someone's indulgence is "being hard on their willingness to comply". The sentenced could be read as "I've a few theories I'm currently pursuing... but before I bother you some more with my theories, may I offer you a drink?"

Yes, you have the right idea: "Before I *try you even more* by *talking* about my projects...".