Six hole cards, split into a Hold'em hand and an Omaha hand right after preflop.
Button and blinds.
Six hole cards. After preflop betting, each player locks in a 2-card subset (Hold'em) and a 4-card subset (Omaha) from their six — that split holds for the rest of the hand.
Small bet preflop and on the flop, big bet on the turn and river.
Pot splits between the best Hold'em hand (using 0, 1, or both cards from that subset) and the best Omaha hand (exactly two of the four Omaha cards + exactly three board cards).