Carlsbad weddings split between resorts and gardens. The resorts along the coast and inland by the lagoon handle larger guest counts with everything in one place, which suits couples with family flying in. The garden weddings are smaller and often at private homes in Olde Carlsbad, where the lots are big and the trees are old. Either way the town is easier on out of town guests than anywhere further south: parking exists, hotels are near, and nobody is fighting traffic.
Spring is the season people plan around. The flower fields above the coast run roughly March through mid May, and while you cannot hold a ceremony in the ranunculus, the whole area gets busy and photogenic at once. Summer brings the marine layer to the coast most mornings and clears by noon. Autumn is the reliable one: warm, clear, and the ocean is still comfortable into October.
North of the lagoon the coast opens up and the wind follows. Ceremonies on the bluff and on the sand at Ponto need the same treatment as Coronado: amplified sound, weighted anything that can blow over, and hair planned for wind rather than against it. Resort lawns set back from the water are calmer and that is often the trade couples make here. Beach ceremonies at state beaches involve a separate permit process, so check the current requirements before booking a time.
Legoland is closer to your start time than you think. On a summer Saturday the traffic in and out of the park and the resorts around it peaks in the late morning and again at closing. If your ceremony is at four in July, guests coming from the south will hit that. Say so on the website you send them, and pick a start time with twenty minutes of forgiveness built into it.