I never heard of the style until now. Sounds almost like a braggot but maybe not quite. Regardless, I do make other honey beers and find that a lot is needed if you want to taste it. So I'd definitely go high on the percentage of honey, like 20% or even 30%, if you want to guarantee that you'll be able to taste it.
Wildflower honey is probably best for the most robust flavor, however the character of wildflower honeys varies broadly because "wildflower" can of course mean anything and depends on the flower sources where it is made. The most wonderful honey anywhere is tupelo, but it is expensive, and might get lost under the 70-80% beer ingredients. It wouldn't be wrong to just use plain clover honey either, but it has a very mild flavor that again could get lost under the beer. So something with more robust flavors like "wildflower" is indeed probably best, as well as being the most traditional probably anyway.
I would add mine at flameout, just because that's so easy to do. However, you can also add near the end of primary, or even might want to consider making a mead on the side, then blending to taste after both the beer and mead halves are fully fermented. This latter option might even be the best way to go, if you want the most control over the finished product. Then once they are blended, don't bottle or keg right away but give the blend a chance to mellow and complete fermentation if it wants to.