I too assumed you would no longer be interested once you found out it was not the type of printer you are interested in. I'll address each point individually. Keep in mind, I am not affiliated with FolgerTech in any way besides advertising and contract work for documentation and design. I do not profit from company sales unless you use our discount code just as any other advertising affiliate would.
I'm not sure this was ever an actual problem. Maybe once or twice from manufacturing errors but I can not recall any.
I also have not heard this issue if the kit was built correctly.
I'm not aware of any holes ever being missed or miss drilled. There was a limited amount of kits sent out awhile back that had a scaling issue on one of the parts. This was instantly corrected once reported and all those parts replaced. I believe they even went through and contacted the purchasers who might have also had the issue with that part.
Yes, there have been some. This is however the third bed that has been used in the kit. These current beds are custom made for this kit and they have a very good chance of being flat. It's not really much of an issue anymore. Keep in mind though, any Chinese bed can arrive not perfectly flat. Unfortunately all manufactures that use this style bed has this issue.
Yes, this kit has had some issues along the way. This is the second version of the FT-5. This second version has major changes to solve all of the major issues with the original version. In fact, the original one was the first affordable 300x300 printer available. This was before Creatlity got into the game and so many others followed. Every common issue gets attention and fixed in future kits. In fact, the control board has recently been upgraded to a 32-bit controller but the price didn't change. I'm not sure they are currently being shipped with the new controller but I'm currently updating the manual to reflect the change.
One thing to keep in mind with Folger Tech however is speed. Being a VERY small company with only a few employees, they are always struggling to keep up with demand. As they are in the US, they could not expand without raising the price. Labor is so expensive here. They always try to help, but things do take time to happen sometimes. If you are OK with this and like to tinker, give this kit a try.
There is a huge community here to help if you have any issues. We have a few VERY active and knowledgeable members here who check the forum regularly. They will have a title after their name like @carefudundae does above (Devoted Member). I hand these titles out when I notice someone who really stands out in that area and has been active for a long time. These members can be trusted. You can also join one of the Facebook groups and get help there as well. I don't think you will have any issues that are not commonly known in the community.