good practices when using gpg --symmetric?

[julio baltazar]

Dear all

Every few months I use GPG to encrypt a bunch of files which I keep as a
backup on other people's computers yet wish to keep private. From reading
the GPG manual, I understand that using GPG the single most important
consideration is a good passphrase.

But I have also been thinking how the following factors affect the security
of my files:

- number and size of files: is there a difference (security-wise) between
encrypting 10,000 small files or encrypting a single, larger archive
containing all of them?

- file formats: should I be concerned about an attacker knowing which format
a particular file is in? Files in a certain format typically have a magic
number in the beginning or have other predefined content.

Are there any other issues one should keep in mind to safely use gpg in
--symmetric mode?

I wish I knew more about cryptography, and sorry to bother you with such
simple questions!

^Julio
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