Xiaomi Corp. declared its ambition for its maiden SU7 to become one of China’s three best-selling luxury electric vehicle models, sounding a challenge to Tesla Inc. and other rivals in an increasingly crowded market.President Lu Weibing cited that internal target for the SU7, which goes on sale March 28, in one of Xiaomi’s more concrete projections yet for its multi-billion-dollar foray into the world’s largest EV market. Xiaomi’s first EV will test both its technological capabilities and a mark...