File Content Conversion in SAP PI

Hello Guru's,

I have couple of questions regarding the File Adapter.

My scenarios are File to Proxy and Proxy to File.

1. File to Proxy.

I have '|'  delimited file with more than 100 fields, But I need to map and send only 10 fields to SAP. And those 10 fields are present first 20 fields only.

Now the question is Do I need to create Source Data Type with all 100 fields or First 20 fields are enough? How do the File Content Conversion if I use first 20 fields.

Pls provide the example.

2. Proxy to File.

In this scenario, Requirement is before FTP'ing the actual file, I need to send a blank file with the name abc.trg. Its like once once the proxy is triggered, I need to put trigger file first and after couple seconds I need put the actual file using Receiver File Adapter. Is this possible using receiver File Adapter?

Appreciate your inputs.