Hello and welcome, @lucasulmer!
This is a completely appropriate place to ask your questions about Hobby and Pro plans. Thank you for reaching out. 
You can find a detailed list of included features and resources in the pricing and limits docs. Those lists include specific numbers for each metric and links to additional information about optimizing usage.
The included usage amounts for Hobby plans are typically enough for most non-commercial projects, but commercial usage would require a Pro or Enterprise plan.
Serverless functions support PHP with a community runtime which is available to everyone. The public repo for that runtime has more info: GitHub - vercel-community/php: 🐘 PHP Runtime for ▲ Vercel Serverless Functions (support 7.4-8.3)