[SalesForce] Not able to complete challenge for final module of process builder

It looks like the Web Email (SuppliedEmail) field is labeled Email Address in the Process Builder criteria builder -- if you click into the field you'll see that the API name is SuppliedEmail. Similarly, Web Name (SuppliedName) is labeled Name, Web Phone (SuppliedPhone) is Phone, and Web Company (SuppliedCompany) is Company.

(I filed a bug about the label discrepancies.)

Try that and see if it works.

Process builder is not meant to be the complete alternative for triggers but it can eliminate some. I see it more as an eventual replacement for workflow. As far as the child records, in Summer 15 there is an update that deals with that, from the release notes here:

Define Additional Conditions When Updating Records

When you update records in your process, you can now filter the records you’re updating using conditions.

To add conditions in an Update Records action:

Select the Updated records meet all conditions option.

Set the conditions that you want to use to filter the updated records.

Example

Let’s say your process updates the status of a parent case when the status of the child case is changed. You can now specify conditions (2) so that, for example, you won’t update the parent case (1) if its status is set to On Hold (3).