How to prune/transplant this sun sugar seedling?

I couldn’t resist buying this sun sugar seedling as it’s the only variety I really wanted to try this year but hadn’t found yet. I am in New Orleans, LA, 9b, and this is my first year ever gardening in any capacity and I am doing containers. I have both a 5 gallon and 10 gallon grow bag available for transplanting, and I’m not opposed to picking up another 15 gallon plastic container if that would be better. The goal would be to companion plant it with basil or lavender and a flower, so I doubt the 5 gallon is sufficient. I know it will need a trellis.

I know it’s important for the leaves to not be touching the ground for the health of the plant. I feel like this is exceptionally bushy for how small and young it is? I’m not sure how much to prune to give it its best chance. I’m hoping the wise tomato folks here are able to give some guidance when I transplant it tomorrow afternoon. Thanks in advance!