You are mixing it up a bit..
NAL isn't structured for making aircraft. They are more of an academic research library who just so happens to have been given the task of making the Saras.
Their research work is what makes them standout.
For an aircraft of that size, the way the Chinese did it is a ideal process to begin with. In our case it would be to have ADA along with perhaps if required, a foreign partner like Antonov or UAC companies, for designing and HAL or Private consortium to manufacture it.
It will require a lot of infra to construct a plane of that size. We currently have nothing of that sort. NAL RTA is a 70-90 seater jet and for that they have requested a total funding of ₹12,511cr. A major part of that is not for designing, but for building the infra required. This is around 20x what was required for Saras Mk2.
For a big jet, it will be even more. Whether such big funds will be approved, well that I cannot predict.
As for the engines, it's not really as difficult as the fighter jet saga we are facing, I think if it's a jet plane, there are plenty of options from whatever country we wish to import for..
