Since you are going to be vaping zero nic, it really comes down to what kind of performance you are expecting. The KR8 will give better battery life and simplicity, but performance does not match the 510. The 510 gives a real smoke-like vapor, and directly replicates that "feeling" of smoking, and vapor amounts are huge. For this reason, I recommend the 510, there's a reason it's the most popular model on this forum

Since you don't require a nic fix and want to vape purely for pleasure, I figure a few extra minutes of tinkering here and there to get a quality vaping experience would be acceptable for you, go 510. It's also less expensive, so you'll have more cash for different liquids.
You want to be a able to change up flavors, which makes cartos a nice convenience. You can drip with the 510 and use carts, so it's a bit of a moot point. Obviously, cartos would be more convenient here.
Good luck with whatever you decide

I can definately vouch for the Cignot $35 no-box kit, it's hard to beat that. I say get one of those to start and some different flavors to drip with and play with, then once you figure out what you like you can fill carts and swap 'em around.