Well, that's a fairly low resistance coil, and you may require more wattage. That tank (and the Smok prince tank) are really more in the sub0hm range, so if you are looking at that type of coil and wattage, I would suggest a higher VG juice (although really that is partially preference, there are sub0hm vapers who use a 50/50 ratio, or even less p.g. I'd say 18 nic may be too high for sub0hm tanks, honestly, I'd consider starting at 9. Or even less. If it's unsatisfying you can always bump up your nic.
The Zenith tank is really a MTL setup, and even with the 0.8 coil you are going really only very slightly sub0hm. That can still be vaped in a MTL fashion, so if you desire trying out nic salts at 18 mg/ml, well, you can probably purchase some premade nic salts at or around that level. I'm PG sensitive so I can't give you a ton of personal advice about PG/VG ratios other than to say that 50/50 seems to me to be a reasonable place to start, again you can play with your ratios if 50/50 doesn't suit. You could certainly try a nic salt vape, although honestly, unless you have a very, very hard time handling nicotine's harshness, it may be equally fine to just use freebase nicotine, depending on your nicotine tolerance. Either would work and would be easy to obtain I'd think. But, if you try nic salts, I'd probably reserve them for your MTL tank. They are more expensive, and (IMHO) there really is no reason to use nic salts in those devices, unless you want to DIY nicotine, and just buy one kind of nic and etc.
You do pay a premium for nic salts, even if you DIY, they are overall more expensive. Most DIY outfits will sell you a sample of nic salts for the cost of shipping, so if you want to try it out inexpensively and have a bit more control over your ingredients, you could get some with little initial outlay, and just buy eliquids that you enjoy but with 0 nic, and then add your own. If that's overwhelming, well, sample some ready to vape nic salt juices and see how you like them.
I just opened a 100 mg/ml nic liter of nic salts, but the latter part of my stash is actually freebase. Since my throat has recovered, I may try returning to regular nic salts, as I'm currently using juice I won at 18 mg/ml regular freebase and having no issues, if it works out, it will be nice not to need to convert them.
Best of luck,
Anna