I started primary 5 days ago. On the second day it had a healthy yeast cake on top. Day three it began to fall and yesterday, so day 4, it went all the way down. The temp is at 70 degrees and is an ale. The airlock stills bubbles but about once every thirty seconds to a minute. I want to keep it in for at least a week, but after day 7 should I move to secondary fermentation?
Use a hydrometer and take a reading at the same time every day for the next three days. If the reading is the same each time, then fermentation should be done.
Airlocks aren't really a great indicator as far as determining when fermentation is finished, so don't rely entirely on that. Also, Sometimes you may not see much krausen during fermentation, other times it will explode!
The beer will tell you when it's done. I used to let my beer ferment for 5-7 days, but I've got a lemon/citrus wine that has been fermenting for 3 weeks now. If you bottle too soon you'll have bombs!
Unless your recipe calls for lots of dry hopping or the addition of fruit, you probably don't really need to do a secondary at all. Pitch yeast, let it rip, wait 3 weeks, then bottle. If the fermention kicks off within the first 24 hours and looks strong, then don't even bother checking gravity for the first 2 weeks (unless you have a strong drop in temp during fermentation, in which case the yeast might stall out).
The old lore of "1-2-3" (1 week primary, 2 week secondary, 3 weeks to condition) is pretty out dated. The top level gurus of homebrewing, and the yeast companies themselves, are more and more recommending AGAINST secondaries unless you have a good reason to do so. Yeast health and ingredient quality have improved greatly since the surge of homebrewing some years back, so you don't have to worry about autolysis and such within 'normal' brewing conditions.
Temperature can definitely affect fermentation. If yeast gets too hot it can die, and if too cold can become inactive. 70 degrees should be in the "okay" range for most ales. While airlocks aren't the best way to tell if your beer is done fermenting, if it is bubbling (even slowly) it is still fermenting.
Secondary fermentation is primarily for clarifying or dry-hopping (hops or other flavors). That really depends on what you want done. You might even notice that moving to a secondary tank wakes up some of the inactive yeast and will ferment a little more.
If you start looking at Cloning recipes you will find out that some brews tell you to wait MONTHS in order to let your beer age a little.
As an important aside, the longer you leave your beer the more the yeast re-absorbs some of the bi-products that can happen during the fermentation process. This will only improve the taste of your beer.