Yeah, over 2 weeks...Sorry I waited, thought you'd have lots of replies with solid recipes above my pay-grade. I'll give it a shot...
I'd be experimenting with with the sweet strawberry and vanilla bean ice cream. Perhaps a 6%/2% or so (straw/van)? Same would go for mango. After that, start adding a few drops of watermelon to the recipes and then doing a crisscross of the flavors. That's how I approach most of my mixing. Just make sure that you start at the low end of percentages as you can always add during the steep, drop-by-drop.
My personal method of mixing is probably rather unconventional, but when I have two basic recipes I like I never burn/re-wick; I just add a few drops of the new recipe to the old in my saturated RDA. Doesn't always work, but I've found a few gems with this method.
Can't help with the menthol as I despise it, but to each his own. Maybe .3% to each recipe would keep you happy?