That's a bit of an overly simplistic answer, and not entirely accurate. 422 and 444 as monitoring modes differ primarily in how you feed them, what your monitor device is, and what you're proposing as a processing pipeline. There are a lot of "indie" projects that are graded in Rec709 and put through a simple transform when the DCP is made. In that scenario, 422 monitoring is perfectly acceptable provided the monitor itself is properly set up. Monitoring in 444 RGB using dual link is preferable, but for most scenes really isn't going to make any appreciable difference. If you're working in P3 on a proper monitoring device (say, a 2K DLP Cinema projector) that changes the situation, but if you're looking at a video monitor, it's not a simple answer like "422 is unacceptable" or "444 is acceptable." There's a lot of room between the two depending on who's doing the work, what they're doing it on, and the level of expectation with regard to an exact visual match to final deliverables, especially when you're talking about no-budget "indie" projects.
Can you adjust gamma on the monitor? After a good chat with one of the technicians at Autocue, he told me a gamma value of 2.6 was good for D-cine work. Take that as a starting point.
When I do things going to XYZ I also set the white point to 6302K, as the preset in the Autocue monitor suggests when you select D-cine color space. Depending on your monitor, this might not be available.
as I understand it, mixing the standards isn't a good idea.
If you want to grade in bt.709 you should set the monitoring to the approprirate adjustment. That will give you a secure foundation for converting to dci by using simply a lut (search this forum).