How do I know which level to purchase?

I need to create event registration for about 5 events annually and collect payment. 

The package to purchase will depend on the number of payment submissions you expect from the 5 events annually. The limits Monthly are as follows;

Bronze: 10 payments/month

Silver: 100 payments/month

Gold: Unlimited payments/month

Enterprise: Unlimited payments/month

You can view all the account limits here: https://www.jotform.com/pricing

For the Enterprise Plan, there is a dedicated page here: https://www.jotform.com/enterprise/

Note that you can Monthly or Yearly.

If your events occur for the whole year, a yearly subscription will be ideal (you get a discounted rate for paying yearly). 

For Monthly, you can pay when the events are happening and later downgrade your account back to free.