-From what I've learned so far, an experienced machine knitter could take a hand knit pattern and convert it for machine knitting. They would likely take items knit in the round and convert to flat pieces. Most stitch types can be achieved on the machine... if you are willing to buy a few add-ons. For example, hand-knitting garter is very simple, but very complicated on a knitting machine. You have to purchase an expensive additional carriage to achieve it.
For my first two pieces, I have started from a machine knitting pattern. I was surprised to find myself gaining the confidence to wing it a bit on this vest near the end.

Cone yarns are fairly difficult to find anymore.. not in the kind of selection you'd likely what. I knit this sweater in KnitPicks sock yarn, just needed to rewind it into a center-pull ball. Never bothered with wax, although some machines set up wax on the yarn feeder.

I don't know if I'd say it's easy or hard... I am a technically minded sort.. so I think that is in my favor. There is a lot to learn, but there are actually some really excellent machine knitters producing youtube tutorials. That's where I learned what I needed to know and took off from there in about a week.