Port a PS Vita game to Steam

Yes, if you made the game or hold a license. You rebuild it in a modern engine and export a desktop build for Steam. Summer Engine generates playable scenes from a description of the original, lets you edit in C++, GDScript, or C#, and exports Windows, macOS, and Linux builds.

Nothing directly, since no desktop input sits behind the screen. Move rear touch actions onto unused controller inputs such as remaining shoulder buttons or stick clicks, or onto a modifier plus an existing button. Mechanics built entirely around rear touch usually need redesign.

Because 544 doubles exactly to 1088, so a 2x scale lands essentially on 1080p. Interface elements and 2D art can double crisply without the blur that non integer scaling causes on other handheld sources.

Almost entirely. The Vita had two analog sticks and a full button set, so movement, camera, and actions map directly. The exceptions are front touch, which goes to the mouse, rear touch, which needs a new home, and gyro, which can go to a stick, the mouse, or real gyro on controllers that have it.

Mostly you raise resolution rather than redraw. One thing to verify is color: the original Vita had an OLED panel with strong saturation and deep blacks, so art authored on it can look flat on a typical monitor. Check contrast and saturation on a calibrated display.