Start in the absolute smallest container and gradually increase size each transplant. First transplant shock is more legend than reality. Ham-handed people that know they are klutzes be advised that by taking your time and knowing what you are doing then even you can transplant successfully. Read, read, and then read some more before asking questions but we welcome those too.
But the absolute prime reaon is the rapid development of a big and healthy root system. Big Steve advocates for this container stuff on here and I openly derided and mocked him for it. On here. Then I was forced, literally, to use a box of 4" planters I had when a blizzard here in AK shut down all unnecessary travel for days. Jesus H Christ. I ran out of the 1 gallon "seedling" planters I had and was overrun with seedlings. Out came the seedling soil and the 4" planters. Let me assure you that by the time all these plants were 1 month old those that started with Big Steve's baby container bit were far bigger and healthier than their 1 gallon sisters.
No secret it's roots before shoots. Use the graduated container method and get them bigger and faster!!!!!