Hi,
Your proposed solutions are not very good.
1. IP changes all the time. If i'm from my phone, or even from home, most people loggon using PPPoE so everytime they restart or loose connection they get a new IP.
2. it all depends on what you are protecting
if it's something the user bought before, it's easy (either if marked as Ok or Fraud).
3. Once detected I could write in localstorage, but tat too can be wiped out, so that is not a 100% against a malicious user
4. what do you want to do with VISITOR dns? you mean potential customer? Even so. DNS doesn't change that often, and if you have the IP, you can check the DNS at a later time.
I assume you want to know the IP owner, network to avoid proxies. This could be done instead with a proxy scrapper that is run once a week to scan a few sites for new proxies + a list of IPs from cheap VPS providers and proxy services (though there may be some users with legitimate proxy use)
5. a much better protection would be to scan social media for the user's name, search if he has friends (and not bots), etc.
If you're interested, drop me a line.
George