A lot of people plant the seed in a smaller pot or cup before transplanting it into a larger pot. What are the downsides of planting it in a larger pot from the beginning? Wouldn't planting it in the large pot from the beginning stress the plant less?
It's not enough stress to transplant once to worry about. Think of every plant sold in stores, they're all transplanted when they get home and they're fine. The only downside I can see is if your final pot soil is very rich or "hot", it could be too much nutrients for the little seed/sprout. Personally I start them in little 4" seedling trays using mild "seedling soil" so that I can keep them handy for watching the watering and keep track of germination easier before they go downstairs in the tent in their final pots. For my soil, I wouldn't hesitate to plant the seed in the final pot, it's just a convenience thing for me. Forget the concept of going up in various pot sizes till the final. That's just internet BS.
we use to do that when seeds were free. Then you would pick your best plants from the cups and plant them and maybe cull the rest.. But no more. At $10 a pop I plant directly in the container it will spend it's whole life in. Why risk any kind of transplanting stress whatsoever?
Autos I plant direct to the 10 liter/3usg pot ...they really don't like to be potted up often tho photos are started in winter and are due to go the whole 6 months in say a 10-15 usg pot so I often start photos in rapid rooters, in warm and controlled indoor conditions then to a 4inch pot them later to the same type 10 liter/3usg pot as the autos then onward and upwards when required good luck