Same-codec re-muxes (e.g. VOB → MOV where both use H.264) produce nearly-identical sizes. Codec changes can swing the size dramatically: H.264 → H.265 typically halves the file at the same visual quality; H.264 → VP9 is roughly comparable.
Up to 8K (7680×4320) on Premium. Free users are capped at 4K (3840×2160) per the file-size limit. HDR metadata (HDR10, Dolby Vision) is preserved where both VOB and MOV containers support it.
Yes — embedded subtitle tracks (mov_text in MP4, SRT/ASS in MKV) are preserved when both VOB and MOV containers support them. Burned-in (hardsub) subtitles transfer automatically because they are part of the video frame.