Phoenix Flower, what Homesteader said, I agree with,
Bigger plant bigger roots bigger yield.
I would like to add to what he said.
While the number of fingers on a leaf do not have any direct effect on the bud size, it is a good indicator of the overall general health of a plant just as the overall size of the leaves indicate the same. The number of fingers on a leaf is determined by multipal factors that include genetics, the age and stage of growth, and health.
Genetics: just as the genetics of a plant determine how wide (Indica) or narrow (Sativa) the leaf fingers will be, the same is true for the overall leaf size and number of fingers. As you gain experiance with differant varieties, you will see these genetic differances. Some plants rarely produce leaves with more than 5 fingers, while others produce 9-11 fingers regularly.
Age and stage: You are correct with your observation of the plant through the seedling stage. It begins with the 2 rounded cotyledon leaves followed by the first true leaves. Normally, those first true leaves are a single finger followed by a pair of 3 finger leaves and then 5 finger, as you saw, but not always. I have had seedlings produce a first set of true leaves with 3 fingers, and wait until you have a seed sprout that has 3 or 4 cotyledon leaves and true leaves, but that's another subjest. In the veg stage your plant will generally reach it's maximum leaf size and number of fingers around the 6-10th set without topping or LST. That size and number can/is also goverened by topping and other LST (low stress training) like tying down the growing tips to allow the branches to grow into an even canopy. After you flip the lights and as the plant goes into full flower production, the large leaves began to get smaller untill at the tips of the flowers, the leaves are back to single, very short leaves known as follicle leaves, that will be covered in beautiful trichomes.
Health: the health of you plant will also determine the size and number of fingers each leaf has, especially during the veg stage. The bigger the leaf at flip. IN GENERAL, the healthier the plant and the bigger the flowers. You may have noticed that after topping, the first set of leaves from the new growth is smaller and has fewer fingers than the old sun leaf at that growth node. NOTE, you never will hear of an experianced grower topping a plant after flipping the lights to 12/12 and the reason is because the plant can't fully recover to produce as much, or as large a flower, as it could have if it had not been topped in/at the flip to flower. IT WILL NEED TIME TO RECOVER and yes, the size and number of fingers on a leaf can be a good indicator of when you plant has recovered and is ready for you to flip it into bloom. (personally, I will not top within the last 7-8 days of veg)
I would also like to commend you on your forthought and planning for heavy colas and if the branches will support them. In general, the same genetic factors come into play. Some varieties will support their buds just fine while other varieties need serious support. IN GENERAL again, the shorter broad leaf (Indica) varieties have smaller and more dense buds with thick stems to support them. Tall and thinner fingered plants like Sativa's will almost certainly need support, so you can plan accordingly. And as for your concern over putting a plant into flower when it is only in it's early veg stage, there is a style of growing that does exactly that. It's callse a
Sea of Green (SOG). It is the ultimately fastest way to get a harvest, but requires covering your grow space with dozens of tiny plants and because of state plant counts, not exactly legal as far as I know in any state, so I'll leave it at that. But to answer your question, yes, those very young and small plants support their single bud and each other in a SOG very nicely.
Hope that helps and keep growing! N2