It just requires an additional assembly line to be setup, the plan was to have 50/year but that was cut back down to lack of orders, etc. Iran needs to work out what a modern air force looks like before purchasing. Iran is geographically a big country, so a platform like the J10CE may be more useful for them than the JF17C which is more short legged. The J-35AE is also of critical importance for them because with the stealth jets, Iran can roam Iraq and Syria and take out the air to air refuellers themselves directly which means that the IAF cannot operate over Iran at all. Iran will need area defence of high value areas, so there is a role for the JF17C if that is the direction that they want to go.
Su-35 may still have value for Iran due to its long range, but the Su57 would be better. However, I suspect Iran has finally worked out that Russia will not work to give Iran any military advantage over Israel due to "so many Russian speakers in Israel now"..
Interms of politics, and optics, it would be far better for FC1 to come from China, than Pakistan as Pakistan can be pressured to stop supplies. China cant as easily.