Try creating a new connection diretly between the <Schema> output port of the FeatureWriter and the Excel output feature type. Also, open the output feature type attributes and make sure to tick the box "Dynamic schema defintion". This will allow the Excel writer to use the schema defintion from the input features.

 For the second question, unfortunately there is no easy way to create dynamic parameters in FME. The parameter values must be known before the workspace is published.

To make those parameters (partially) dynamic?

One of my colleagues asked me to build some functionality to add extra items in a pulldown parameter.

I was used to do things like this in Excel: Userform in VBA and fill the pulldown on demand pretty easy.

In FME it took me queued some time to figure out this one. But the solution was surprisingly simple:

When I discovered that *.fmw are xml’s, I started to redefine the problem. After a successful test on reading and writing fmw-files as text files with an alias (*.fmw) extension, I only had to update the file on the server. And that’s easily done with a HTTPCaller. All though its partially dynamic (user has to update workbench in advance with a separate service), it gave my colleagues the opportunity to update the pulldown list without me updating the workbench for them.

I hope this idea will help you too. Good luck.

Another (probably more useful) method I’d like to share:

In this method there are two Workbenches needed. 

The first Workbench gathers the choice options found in the by the user uploaded source file and will create a HTML where these options are summarized in choice lists presented to the user as questions with a dropdown menu. In the screenshot below the needed HTML. (Tip: by using Data Streaming on FME Server the HTML will open in same browser).

I used a pythoncaller to build the choice lists. And I included a parameter with the location of the source file, to tell the second Workbench where to find it. One important thing to know is that this file location parameter (string) can’t be added directly in the API’s URL, therefore it must be encoded to BASE64

After the user submits his/her choices, the HTML is using a PHP File (to be stored on your web server) that will send a request to the API of the second Workbench. In the screenshot below the code I used. The parameters that are part of the second workbench are part of the API URL, so these have to be filled in. I chose a method in which the individual parts are concatenated in a join action.

In the second workbench the file location parameter has to be decoded to UTF-8 and then the source file can be read again. And after that you can do whatever you want with the gathered values in parameters.