The Garden Inn is at Harbor and Chapman, about a 10 minute drive from DL. It just depends on how many red lights you get, and how much traffic. At DL opening and closing it will probably take longer to get up and down harbor, also if there is something big happening at the convention center.
KFC is on Ball Road between Harbor and Anaheim Blvd. It's not far from DL at all. It's by a McDonalds (it's eaiser to see the McDonalds than the KFC. The closest to the hotel is at Harbor (opposite direction from DL) just before Garden Grove Blvd.
Cheesecake factory the closest one is at the Brea Mall. Take Katella or Ball (from DL) or Chapman from hotel to the 57 freeway, go North, Exit at Imperial Highway, Turn Left onto Imperial (West) and the mall is on your right hand side at State College. It is in the mall parking lot. You enter the parking lot from State College, and the restuarant is up by Imperial. There is also one at Beach Blvd and the 405 freeway, if you are driving that way to get to the beach. There is another at fashion Island in Newport, and another at the Spectrum in Irvine.
To get to the beach there are lots of different ways to go. Basically you either need to take streets all the way up to the beach or jump on the freeway. (which kind of takes you out of the way). If you want to go to Huntington Beach take the 57 South to 22 West and get off at Beach Blvd. Then drive South and you will enter the Huntington Beach, or you can drive along PCH and drive along the beach. To get to Newport Beach take the 5 south to the 55 south, this freeway will end and you just follow the road to the beach (the alternative is to take Harbor Blvd, and it will take you to the same road). It's at least a good half hour, and probably longer. On warm days, it take take half an hour to go a few miles down near the beach.