Regarding #1 above, probably never! However, DreamHost is having an awesome sale to celebrate their 8th year in business! They'll give you a whopping 80% off your first year of service, but only if you sign up under the yearly payment plan. If you're interested you have to act quickly, however, because they will end the sale once they've acquired 888 new customers. Also, you have to be sure to enter "888" in the special promo field if and when you sign up... For full details, go to the DreamHost home page and see if the sale is still going on!
Regarding #2, fret no more, my friend: DreamHost has changed it's policy to unlimited domains on all it's hosting plans! Awesome, huh!