Since you already have a coinos account, then just copy the lightning address and also paste it into the Nostr address field and it will show you as a verified user...
Few things:
1. get a check mark in #Nostr, there are few options, I suggest nostrcheck.me, once you get it, edit your profile and update your Nostr-Address, not having it will hide you in some clients
2. follow hashtags, a good way to find like minded people
3. think of your nsec as your Bitcoin private keys, act accordingly
4. chose a client that respect your privacy, meaning, you can sign in with a Signer protecting your nsec, it has TOR built in and above all, you can manage the relays you use. I suggest nostr:nprofile1qqs24yz8xftq8kkdf7q5yzf4v7tn2ek78v0zp2y427mj3sa7f34ggjcpzamhxue69uhhv6t5daezumn0wd68yvfwvdhk6tcppemhxue69uhkummn9ekx7mp0qyg8wumn8ghj7mn0wd68ytnddakj703s8dt t
5. add your lighting address in the profile so you can get zap, few options out there, I suggest nostr:nprofile1qqst4qyeqenw7zm0fwjsty68h6cnys5jre2xd8ngqpjv5a2j26s78fspzemhxue69uhhyetvv9ujucm0d9hx7uewd9hj75a0pev for most people
have fun!