If I upgrade to the bronze plan, how many people can get the notfication email when a client fills in our training request form?

For the paid accounts, you can add 10 email recipients in the notification email. The limit is 10 email recipients per notification email. 

If you need 17 email recipients, you need to create 2 notification email. Here's a sample:

Notification 1 with 10 email recipients
Notification 2 with 7 email recipients

To add a new email recipient, go to the Recipients tab and click the "Add New Email" text link.

I hope this information helps. 

Yes, thank you Vincent.