Using KiCAD's tools to generate files for board assembly

[LoveLaika]

I'm trying to use some features in KiCAD to generate the necessary files for PCB assembly. Previously, I only done boards, so I generated GERBER files and drill files for DFM checks. However, as I'm now getting into contracting out assembly, I'm at a loss on how to proceed. I was wondering if you guys ever used KiCAD to generate necessary files for assembly? If so, how can I do the same?

For starters with regards to companies, I'm looking at JLCPCB and Advanced Circuits. JLCPCB seems to be pretty popular here, and Advanced Circuits seems pretty reliable. I previously had boards done by the latter but not the former.
With regards to my board, it's a 4-layer board with components on two sides. I heard that JLCPCB only does single-sided designs, but is it possible to assemble just one side of my board only? I would hate to have to make modifications.

For Advanced Circuits, here's their checklist of what they need. The GERBER files seems simple, but how do you use KiCAD to generate the rest of the files? There's so many options for BOM, and the other files seem foreign to me.

EDIT: After playing around, I found some notable issues with some of the tools.

Basically, from what I gathered so far, the best way to generate a BOM is through EEschema's tools. Generating a BOM in PCBnew results in a messy CSV with columns separated by a mixture of tabs, semi-colons, and quotes. It's quite a mess. Then again, EEschema's BOM is rather large. The options fail to add an extension to the resulting file, and you can't rename the files beforehand making it difficult to track.

Looking at PCBnew's Footprint Position file generator, it doesn't appear to include all the footprints. I had some footprints with the prefix "J" for input/output/power connectors and whatnot, but they didn't show up at all in the generated file. Plus, the coordinate system in the Y-direction appears to be the opposite of how PCBnew works. If my component has a Y-coordinate that's positive, the generated file will show that as a negative value instead. 

These little things are making me very confused as to how to prepare files for PCB assembly.