Looking for information for phone/cell service when I arrive, have an iPhone 13, I’m assuming I can just buy a Sim card, prepaid/preloaded? 
TLDR : Answer Summary
When arriving in Thailand, you can purchase a prepaid SIM card for your unlocked iPhone 13. It's recommended to buy a SIM card from local stores like 7/11 after immigration rather than at the airport, where prices may be higher. Popular options include AIS, which is often recommended for expats. Additionally, services like eSIM can be used, and you might consider a VPN for security while online. Plans generally cost around 150-200 baht for 30 days.