I'm not going to tell you how to run your business but I'd wait until you finish the updates you have planned. After you finish the main game, I'd work on DLC and sell those separately but the main game has to gather a crowd for that to work.
The beginning of the game starts out really good. You work to progress and fit your ship, gather your crew, corrupt the girls etc. The moment you jump through the jump gate, things slow down. In Arellarti, there are things to do but the Dome is not open for example, which will probably be in the next update from what I read. This is good because it brings content to that next system, bringing it in line with the first in terms of content.
Then we move on to Xenos and things slow down even further. There is only a station, an asteroid field the library from which you get your one and only mission if I remember correctly. There's no bar, nowhere to go on the station, no people to meet etc. The system is pretty barren. After you do the Krell update, I'd focus on Xenos a bit and go on to all the other systems after that and fill them with a bit of content, bringing them in line with the first. Speaking of Xenos though, I love the music in that system, especially when going from flying around to engaging in combat, awesome!
I haven't made it past Xenos yet so I can't comment on the other systems, but that is my observation so far from what I've played. So in short, I'd work on it another year or so and fill the game with content, but leaving the end as is. After that, I'd do expansions that expand beyond that ending.
If you manage to hook people on Steam, they will be hungry for the expansions. I wouldn't put the game out in this state though on Steam. Once you know the ending, it's hard to go back with the same suspense and play the content you added in between. I'm actually considering not going further than Xenos because I don't want to know the end before I experience the rest.
All this is just some food for thought of course, some feedback. I've played hundreds of these AVN games and there is only one that offered me as much content and playtime as this and that is Being a DIK. As I said in m last post, you got a good game going here, I wouldn't cut it short because it has great potential. I'd personally work on it another year or even two before going big on Steam. I have no doubt that if you went down that route, this game could easily compare to the best of them.