Multipliers are only used when you trade contracts. If you trade the DAX future directly on an EUR account, use LotAmount = 25, Pip = 0.5 and PipCost = 12.50.

The USDJPY is already in the IB asset list, so you can just take over the parameters. MarginCost is not used by IB, they use Leverage instead. AFAIK the forex leverage is 33.