1) I'm not an expert, but I don't think Apple can really pull the plug, as the boot loaders are basically linux emulators that work very well. Apple does make things difficult though, for example, to get iMessage working, you need to follow a host of things like changing UDID, making sure serial numbers don't clash etc, so to get a 100% working Hack can take some time
2) Generally speaking, Intel processors are used, avoid i3, but any i5/i7 and certain Xeons can also be used. When it comes to GPUs, I would go for Nvidia as Nvidia have good driver support, I used to have an ATI card, but that gave problems when waking from sleep. Skylake processors have just received native support I think so should work without any special kexts, I don't think the 1070 can be used right now, but should be available soon as long as Nvidia release drivers. People are using the GTX 970/980 though.
3) You may need to upgrade say the Wifi Card, ethernet card, GPU etc, but generally speaking the mobo and processor should be fine, I'm still rocking a 3770K and a Gigabyte Z77-DS3H since around 2011, and I had a 2500K before that. I originally used a ATI 5770 but with El Capitan it gave problems, so I bought a used GTX 760 and everything has been fine. Before that I used a Core 2 Quad since around 2009 with a motherboard I didn't even intend on using as a hackintosh, but had really good support anyway.
My advice; if you're going to use the Hackintosh to make money, through video editing, programming etc, and you can't afford downtime then I would seriously reconsider it, and maybe just get a used rMBP with applecare or something. I for one am a student so have time to tinker etc, but I graduate soon and when I get a good job will buy a Mac Pro or top end rMBP 15 for my desktop use, as tinkering with Hackintoshes for the better part of almost a decade now, I'd rather just have a system I could turn on and not worry about sleep or audio not working etc.
Tl;dr - If you have time, want to learn about the ins and outs of a OS X and don't mind some command line coding for fixing things like imessage/audio etc, then by all means look at tonymac86.com, look at the golden builds and recommended parts and get hackintoshing. If not, get a proper mac and enjoy it!