To be honest, I am surprised you got any response at all. Most wgs are only interested in enquiries stating date; time; and how long. I suspect most would consider an email asking if they would like to be added to a list for some vague time in the future, a waste of time.
I think you're going about it the wrong way. They won't be sitting by their laptops all day jumping up with excitement when they get a new email saying that a potential customer might consider them!
If you have specific questions, such as details of services provided, hours they're available etc, which are not specified on their profile, then of course it's worth asking before making a decision. Then once you've found one you like, ask them if they're available when you want.
If you're having trouble choosing, "run the numbers" here on UKP: every AW profile has a number- copy and paste it into the UKP search box and any reviews from members here will come up. These are invaluable in weeding out the time wasters!