As for location, if you want a theme park or shopping you can't go wrong. There's even an artificial beach and waves in the massive lagoon pool at the theme park if that's your thing. I should say that entry to the parks was very reasonable - A$13/£5.50 got you into the water park with lots roller coasters and the like as well as the extreme park with ATV safari, paint ball, kayaks and the like, and there is a wildlife park for a small additional charge (as with all such places, they made up for the low price at the food and drink stalls and lockers which had to be fed each time you opened them).
There are 2 big supermarkets in the shopping mall which are open 10am to 10pm and 24 hour convenience shops outside the main entrance, where you also find several tourist and local restaurants and lots of canteens. The canteens and even food stalls with their fixed, marked prices are maybe 20% more expensive here than other places we've been, and get the occasional adventurous tourist wandering in. Two of the ones we went into overcharged us - one only slightly, unusual for Malaysia but not worth quibbling about, and one by quite a lot percentage wise (we're only talking a dollar or so, but it was double the price we should have paid). The system of charging you by what is on your plate is quite arbitrary although usually very honest and even after I questioned the amount of the bill at the second one they stood their ground. Once you've eaten the food, there really isn't anything you can do except not go there again. Much better is to walk for five minutes or so and get out of the Sunway Lagoon area where everything was priced normally and honestly. If you prefer, the shopping mall has every brand of fast food/restuarant/coffee shop and a food court in each of the supermarkets.
There are lots of buses going into KL for less than 70c/30p and a taxi voucher system at the main entrance to the shopping mall. The taxi drivers that congregate around the hotel entrances quote ridiculous prices for short journeys and if you manage to find one who will use a meter, there's a good chance of going from A to B via Z.