A gallon of honey is about 12lb, so that would be added to 4 gallons of water, not 5, if the intention is to make a 5 gallon batch.
To achieve 18% ABV, you will need a drop in gravity of about 132 or 133 points, so if you haven't got a starting gravity IRO about 1.130 or so, then you probably won't achieve 18%, hence you want to think about what type of mead you might want to make. If you're not familiar with meads, then I'd suggest you consider a medium one with a final gravity of about 1.010 to 1.015 - how you achieve that is up to you i.e. either fermenting to leave some residual sugars, or the much easier method of fermenting dry and then stabilising and back sweetening.....
As for the cherry mead idea, you'd likely need much more than 1lb to 1 gallon, something like 3lb to a gallon - and yes it would probably be better to make the mead as a traditional first, then add the fruit to secondary. The fruit is likely to have to be tart cherry, to achieve a good flavour, but you probably still need to think about back sweetening.
Also, there's no mention of nutrient, energiser, etc etc, so I suggest a good read of the Gotmead NewBee Guide
first, to get a better grasp on nutrition for the yeasties.
Oh and I certainly wouldn't use a champagne yeast, as they're notorious for blowing a lot of the aromatics (and some of the more subtle flavouring elements) straight out the airlock.
Either way, your mead, your choice in how it's made, we can only give you ideas/suggestions etc...