PCBgogo

Hi all,
As I wrote on other posts, I am planning to purchase a smt line. I've done all my part from an engineering point of view but now I have to wait for other issues to be solved, such as resolving problems with the location where it will be installed, power upgrade, esd floor, business related issues, etc. In the best case, line will be purchased (if will be) in the second half of this year. The equipment considered for now is paste mixer, printing machine, pick and place, oven and some bits (conveyor, feeder carts, etc). No budget for inspection for now, it will be done manually. Maybe in the future, some inspection machines will be considered for purchase.
Until then, I would like to ask for some help to better understand this subject with inspection because I have some gaps in knowledge.
AOI, from what I have seen, mainly used at the exit of oven to inspect final product. SPI seem to be ignored in many cases and AXI for those who can afford and where is a must (BGA).
My questions are:
1. AOI and SPI seem similar tasks. Is is possible to use generic AOI machines for SPI ? Or is SPI some sort of 'extra' function or option for AOI machines?
2. AXI is used definitely for BGA but recently I have seen some defects specific to QFN packages, which I use a lot (voiding on ground pad or inconsistent paste depositions on QFN edges) which are impossible to detect at AOI, they are under package. They can be seen on AXI only. Is (in this case) AXI preferred for QFN also? Or considering that many QFN specific defects are originated in paste process, a good SPI will solve problems in such a manner that AXI won't be necessary anymore?
3. For paste printing/pick and place/oven there are chinese companies whose products are reliable enough to a certain degree for production. I would like to know if there are similar companies for AOI, SPI and AXI machines and who are those.
Thank you.