b, paragraphs should not be indented in memos.
Generally speaking, you don't indent the first line in memos, cover letters, or other kinds of professional correspondence. Instead, most style guides advise writers to leave a line of space between paragraphs. You can do this by manually adding an extra line after each paragraph, or by setting your word processor to insert one automatically after you hit "enter".
Memos also usually include fields for who the memo is from, who it's to, what the date is, and what the subject is. The format you're probably familiar with from emails include the same fields, so thinking about what gets added at the top of an email message can help you remember how to start a memo. For example, this one might start
October 23, 2012
Re: Formatting memos
For more on cover letters and applications, see the link included below.