Under $4k budget build LA360 build

Sounds like you are well on your way!
What your 3 things add up to is pretty much personal choice. What does your engine builder suggest? Carbs are pretty much a personal thing; I'm a Holley guy myself but to each his own. And a carb swap can be easily done if you're not happy with the results. What does your engine guy say about the TC and pistons?