Bids:
1♦ = nat 3+ or preparatory with 15-17 balanced
2♦ = nat ~5-9 and 5+ diamonds
2NT = shows 15-17, need not have 3 diamonds...
Your bids now mean:
Dbl = optional, max hand in context and defensive values
3NT = on a wing and a prayer
4/5C = nat 54 or better
4H = undiscussed, but will probably be taken a singleton by pard
BID?