What do you mean by converse in a basic but fluent way? Your definition of this may be drastically different from others.
For me, conversation will not be all that interesting, if I can’t understand most of a typical conversation between natives, or even basic movie/tv level. I don’t feel like I have to speak at that level, but I feel like I should be able break into the conversation and ask a question or add something without sounding like it came from left field or totally off topic, or indicated I wasn’t really understanding what they are saying (unless I’m asking because I didn’t understand something =) ). I don’t necessarily need to understand EVERYTHING and I’m sure there would be some topics that I really may not know what they are talking about but still mostly follow along. That to me would be a very basic fluency. I don’t feel I’m there at 22,000 LingQ words and 300 hours listening.
Basic fluency to someone else might mean being able to order food, book a hotel, get/give directions, express basic feelings, talk about weather (Essentially A1/A2 level stuff). I don’t consider that basic fluency, but you might. That kind of stuff I could do at a much earlier level, albeit currently probably in a very hacked up kind of way, but I could get the job done (I barely practice speaking at this point, but have handled these or similar scenarios before). Even in these basic scenarios you can be thrown off if the native asks you anything that is “off script”. That’s where listening needs to the most important part of conversation.
In short, I don’t think you need to wait to speak or participate in conversation. That’s really up to you. Anything you do here is going to help your speaking ability. However, without enough vocabulary and listening practice, you are going to be super lost in any real native conversation. At least that’s been my experience. I feel like I could answer just about anything in some way, but I’m frozen up if someone asks me something or comments and I don’t understand what they just said…can’t speak then, other than to ask them to repeat, possibly slower. But if it’s vocabulary you don’t know then you’re somewhat stuck.