Since Calvin answered two of your questions, I'll answer the remaining.
It is possible to not enter the password in Kmail, most email clients offer to store the password.
In the Kmail settings, go to Accounts and click Add. You'll have the option of POP, IMAP, or Disconnected IMAP. After entering the details at http://support.google.com/mail/bin/answer.py?hl=en&answer=78799 (for IMAP/Disconnected IMAP) or at http://support.google.com/mail/bin/answer.py?hl=en&answer=13287 (for POP) (make sure to enable either POP or IMAP in your Gmail settings in your browser!), tick off Store Password, Show Only Serverside Subscribed Folders, Include In Manual Check (optional), and Enable Interval Checking (optional). On the Security tab, select "Use SSL" and "Clear Text".
When you apply the settings, it will either bring up KWallet or ask you to confirm storing the password unsafely (depending on whether or not KWallet is installed). If it brings up KWallet, and you /don't / want to use it, just click Next, then Finish (don't set a KWallet password if you're not going to use it).
For sending, enter the smtp details on either of those links. For security, select TLS (/not/ SSL) and Plain.
For IMAP, POP, and SMTP, you need to use the full email address as the login.
Ark Linux webmaster
P.S. If you're not sure the difference between IMAP and Disconnected IMAP, Disconnected IMAP (AKA Cached IMAP) downloads all emails. This causes it to load slowly when you first setup your IMAP since it needs to download everything and each sync will go slightly more slowly if you've received emails. The advantage is that your downloaded email will still be accessible if something happens to your Internet connection. If you don't need it to download attachments automatically, you can disable that elsewhere in Kmail yet still have Disconnected IMAP (it will download the text only).