Is it possible to do online tickets for respondants to print out after purchase and add barcodes?

Yes that's possible.

If you want to sell tickets online, you can use any of the available payment tools. This article will give you that information https://www.jotform.com/help/47-Order-Form-Basics. 

To let the users printout after the purchase, add an autoresponder notification in your form so user will receive a copy of the information through their email. They can then print out the message over email.

Or you can also place information along with their data on your thank you page, so whenever the payment is completed, they will see information to be printout on the thank you page.

Can barcodes be added?

We do not have barcodes widget but we have QR codes widget. Check this http://widgets.jotform.com/search/qr.

But if you want to use barcodes, you can use this site to generate barcodes http://www.barcodesinc.com/generator/index.php then use the submissions ID tag {id} as the unique barcode key.

Example:

http://www.barcodesinc.com/generator/image.php?style=197&type=C128B&width=330&height=80&xres=2&font=4&code={id}

Simply paste this link as an image on notification or thank you page, whichever you prefer. This will generate a barcode image after the form is submitted.

Hope this helps!