Saguaro is probably single most recognizable species of cactus— think of the cartoons from childhood.
They live to be very old and very tall- 150-300 years and 40ft tall.
Give it full sun and let it dry out between waterings. Probably hardy to 25F but mine don’t get below 40F typically.
Your seedling is a few years old and is about 1-1.5” tall— Saguaros can be slow growers. Your plant will be similar to the ones in the smaller picture. Yours will ship bare root.