From McMurray hatchery's chick care instructions:
"Hang the lamp 18 inches from the floor. The temperature directly under the bulb will be higher than 90 degrees but the birds will adjust themselves to the area they like. Use one bulb for every 50 chicks in cold weather. Use one bulb for each 100 chicks in warm weather."
https://www.mcmurrayhatchery.com/faq.html
From Ideal Poultry's chick care page:
"one 250-watt heat lamp with reflector for each 50 babies. It is never wise to depend on only one heat lamp, so for insurance, provide at least two heat lamps regardless of the number of babies. Red heat lamps are preferred as they provide ample light without providing excessive light that may lead to picking. The heat lamps should be hung about 18 inches above the top of the litter."
https://www.idealpoultry.com/poultry_care
I would probably plan on having at least one spare heat lamp and bulb, no matter how few or how many chicks, in case a bulb or lamp breaks, or in case unexpected cold weather makes them need more heat.
Once the chicks have had a few hours under the heat lamps to warm up after shipping, you should be able to adjust the number of bulbs based on the chicks' behavior. They might need more or less if conditions are unusually hot or cold.
How many chicks are you planning to raise?
