I can't help with advice on the suitability of the D4 19s for the D5 but would suggest you use 20" rims as you will get more choice in tyres. Do some checking on what you can get with 20's vs 19's I think you'll be surprised.
Have read through these two threads to get you started:
AT tyres All New Disco5
Discovery 5 - 19 or 20 inch LR wheels
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