Yes — the resize option scales the input down before frame extraction, which dramatically reduces final GIF size. A 480p GIF generated from a 4K MKV is 16x smaller on disk than a 4K GIF. Cropping is handled in a separate /trim/ or /crop/ step run before the conversion.
Animated GIF supports single-colour transparency only (a binary mask). Animated WebP and APNG support full 8-bit alpha. Most camera-captured MKV sources have no alpha channel anyway, so the GIF comes out fully opaque regardless. If you do have transparent input (screen recordings, animated rendering output), target WebP or APNG for the GIF.