The first colonists will of course need to bring stuff with them, but it doesn't make sense to assume they won't plan on building most of what they need once they get there. It is a lot easier to setup manufacturing when you don't have to invent the assembly line.
I can maybe see trade of one of a kind things. It hard to believe the Mona Lisa would ever leave earth, but that type of thing where the original is the thing might be worth it. Not enough to sustain trade though, the time line is far too long.
IMHO, first thing sent will be a universal Assembler, which will produce stuff and clone colonists. If a woman can give birth to a baby in 9 months, we can create a "3D printer" which will self assemble other "3D printers", which then produce mechanisms, computers, and colonists.
The "protomolecule" from the Expanse series is an even more effective if frightening version of the idea, an interstellar virus that hijacks any local biochemistry to bend it to its purposes.
> It is at least possible that a manufacturing ecosystem would be so difficult to develop that it would require fewer decades to transport products than to develop that ecosystem.
Or there are multiple desired products whose manufacturing ecosystems place such a burden on a system that a single system can't support them all.
Such comparative advantage would likely disappear overtime, unless a given solar system actively keeps its technological know-how secret in some way, or controls the travel of skilled people (as in nuclear tech today). Or, perhaps, some solar systems may fail to create the institutional context necessary for building such a system — if, for example, they keep nuking themselves. In any case, it's not too hard to imagine scenarios in which such trade would be necessary.