A. No. Steam only offers the paid, up-to-date version (0.990+). The legacy free version is standalone.

For the first time, Space Engine includes a functional starship flight model. You can pilot a small survey vessel using keyboard and mouse or a HOTAS setup, complete with a heads-up display (HUD) showing velocity, altitude, and orbital trajectory.

starting with version 0.990. While older "legacy" versions (like 0.980) were available for free, version 0.9.9.0 and later are the premium, actively updated builds.