4) If you have a raim warning below the MSA you may continue at that altitude to the MAP. ( I think this is an old rule, as JEPP DGA procedures, 1.5.1.f states if there is a raim warning or any doubt off the gps information, a MA must be conducted)
Sounds like a more practical interpretation of the rules than a technically correct one. I guess in theory if you've descended to your current altitude with RAIM available and then it drops out, the altitude you're at is definitely still safe because you got there using valid distance information. The steps always get lower on a DGA so your current altitude would continue to be safe until you reach the missed approach point.
It does also state (and I dont think you'll find anyone who will argue with this) 1.5.2 e. In the event of a significant disparity between the NDB or VOR track, and the GPS track indication, the pilot must discontinue the arrival procedure.
Without raim you have "no" track indication so as far as I'm concerned thats a significant disparity.
Interesting note though it does say you much discontinue the arrival, for which there is no deffinition, however the Missed approach procedure is defined as
The procedure to be followed if the approach cannot be continued.
If you are discontinuing the arrival then surely that meets the deffinition above and hence you must conduct the missed approach. Why it doesn't just say that? I dont know.
Other:
5) You must join an instruments approach at of before the IAF. Never found a rule for that one, and I dont see why it is not safe to join after if you are not descending below the MSA.
This has an approach specific answer however its the only approach that gives reference to it.
(from my old AIP because my jepps are at work)
DME arc:
ENR 1.5 2.8.1 DME arcs must be joined at or before an IAF and at an altitude not below the relevent MSA or the appropriate sector DME arrival step
Obviously if its a reversal you have to fly over the fix but with regard to DME arrivals (track specific) the only significance I've found is for your speed limitations. Finally an RNAV has an Initial waypoint and thus a part of the procedure.