> Starting from the complete bottom just seams over the top. Is it really?

"What I cannot create, I do not understand." - Richard Feynman

And to clarify, currently the ribosomes are provided as part of the cell-free transcription/translation system. Additionally, amino acids, tRNA (plus tRNA synthetase), RNA polymerase, and a primitive energy source (ATP with some extra energy in creatine phosphate) are all provided.

Here are the components of the most common cell-free transcription/translation systems (PURE): https://www.nature.com/articles/nprot.2015.082/tables/1

Yes. Starting from the bottom, we might in the process discover that 90%-99% of cell components are cruft/inefficient, and discover how to make cells 10 or 100 times smaller. Imagine being able to inject neurons in the brain that are 100 times smaller.

Starting from the bottom means, you really did understand it all, once completed ..

Oh, I would say many researchers have that goal, but probably not many would consider it a realistic goal to be achieved in their lifetime ..

(all assumed, biology is not my area)

If you can figure out how to go bottom up, it will result in new innovations in microscopic manufacturing methods.

Or... you can just use the top up built cell to manufacture things. Why build your own nanorobots when there are pre made nanorobots that already works.

Because switching to a different chemical composition (not carbon based) is more likely that way.

I think it must be possible to create equvivalent functionality from more durable materials.

This certainly is scify, but imagine changing all your cells one by one to cells which can withstand wider temperature ranges, and corrode (rot?) half as easily.