Here is their website with lots of info. -
Things to do in Yosemite
Sequoia National Park is actually 180 miles away, but Yosemite has it's own Sequoias in the Park - The Mariposa Grove.
If you like the mountains, and hiking, and being outdoors, I don't think a week is too long at all. If you are looking for more touristy attractions, rather than hiking and natural beauty, a week might be too long.
There is plenty of natural beauty to keep you busy for a week, and frankly, not much else close by.
My must sees are:
To get your bearings you might like to start out with a guided tour.
Glacier Point
Mariposa Grove
During summer I like the lazy rafting on the river
I like the evening Ranger talks
Lots of Hiking
Visit all the waterfalls
Visit the Museums
If a week is too long, consider doing 4 days in Yosemite and 3 days in Tahoe. Tahoe has casinos and restaurants, a beautiful lake, and more tourist attractions. It's fun too.