Tou can still use speed dials with dial from home screen disabled. I just tried it. I have one assigned to the L key. If I press L quickly from the home screen, it brings up calendar. If I press and hold it, the speed dial works.
To disable it, go to Phone > General Options > set Dial from home screen to no.
You can compose an email from the Messages folder. Menu > Compose Email. It will send it from your default email address, but you can also change it to send from any email account by highlighting [Default] and click Menu key. You can also send an email from your contacts/address book by going to that contact, highligting it, menu > Email 'contact name'.
With dial from home screen disabled, you can get to contacts by pressing A or C. I don't have Yahoo mail, don't know if there is a shortcut for that. Some apps use keyboard shortcuts too. PocketDay uses Y.
Somewhere here there are posts with all the home screen shortcuts. It's also on the Help on the device, but it's so darn small I can't read it. I think the user manual is on the disc that came with the Tour, so check there -- it has all the shortcuts and lots more basic info. There are also shortcuts within each app.
You can also read or download and save the manuals here: BlackBerry Tour 9600 Series - Manuals and Guides
Also check out our BlackBerryFAQ if you haven't already for some good tips.