I can’t speak for INS, but I’ll give answers based on my knowledge thus far.
Infinity, formerly Infinity: The Quest for Earth is the MMO that I-Novae plan to make if their current in-dev game, Infinity:Battlescape, and their engine is a success. In order to fund the remainder of Battlescape’s development, they’re looking to run a Kickstarter campaign in the coming months
In the MMO, I believe the intention is that the number of systems will be comparable to the estimated number of solar systems in the Milky Way, which likely means many millions of systems.
Both games will have you flying in ships. The ability to walk outside ships, especially on planetary surfaces, have been discussed many times, but never confirmed (to my knowledge) as a feature by INS
Both games are intended to be multiplayer. It’s unlikely they’ll add a singleplayer mode,