It sounds like a good idea, but I don't think it will work practically.
这个主意听起来不错，但我认为它实际上行不通。
It sounds like a good idea; let's look at the practicalities and work out the costs.
这个主意听起来不错。咱们来看看实际运作，计算一下费用。
I know it sounds crazy but it just might work.
我知道这事听起来很蠢，然而也许就会奏效。
I know it sounds corny, but it really was love at first sight!
我知道这听起来像陈词滥调，然而的确是一见钟情啊！
I know it sounds trivial, but I'm worried about it.
我知道这事听起来微不足道，但我还是放心不下。