Hey Raina,
Thanks for reaching out!
First, you do NOT need to get Events Calendar Pro to use Event Tickets Plus. 🙂
Next, when it comes to SSL you generally do not need it if you are going to use PayPal. See this page on the WooCommerce documentation: https://docs.woocommerce.com/document/paypal-standard/
To quote it directly:
The payment is made offsite on the PayPal website and not your checkout. Adding an SSL certificate is optional but definitely encouraged. More and more an SSL certificate is becoming a ranking factor in search results, and it keeps any information transmitted to and from your site secure.
If you use other payment methods, you will likely need SSL but not for PayPal.
I hope this information helps!
George