Gmail labs: Can you create custom shortcuts involving Ctrl + or Alt +

Google has heard you and there is now a hyperlink shortcut in Gmail:

Ctrl + K (Cmd + K for Mac users)

It works only if the cursor is in the message field, not in the To, Cc, Bcc or Subject ones. And, in Chrome on Mac, it works even when the shortcuts are disabled.

See here.

This shortcut is not yet documented in the official Gmail keyboard shortcuts list, so don't look for it there.

Yes. See the note on point 4 below.

Gmail's filters allow you to manage the flow of incoming messages. Using filters, you can automatically label, archive, delete, star, or forward your mail, even keep it out of Spam.

To create a filter

1. Click the down arrow in your search box. A window that allows you to specify your search criteria will appear.
2. Enter your search criteria. If you want to check that your search worked correctly, click the search button.
3. Click Create filter with this search at the bottom of the search window. If you need to verify the search results, you can click the x to collapse the filter options. Clicking the down arrow again will bring the window back with the same search criteria you entered.

4. Choose the action(s) you want the filter to take.
   
   To keep organized, many people like to have incoming messages automatically labeled and removed from their inbox until they can look at them later at a more convenient time. If you want to do this, make sure to select Skip the Inbox (Archive it) and Apply the label: when you create your filter.

5. Click the Create filter button.

Also,

To use a particular message to create a filter

1. Select the message in your message list.
2. Click the More button, then Filter messages like these.
3. Enter your filter criteria in the appropriate field(s).

From the Gmail help page on using filters.