I understand the time lines and the fund limits, instead of making a sequel, perhaps sell the future content as DLC? That would be less work for you folks than to have to build a whole new game from the ground up.
Viewing post in Ideas for the game (Base and playability value)
DLC is definitely a possibility.
We will launch on PC and in English only and my guess is that the immediate work after that will be around localizing to a few different languages and getting the game on to consoles.
We'll have more thoughts on DLC or sequel and probably a definite plan after launch.