Corus hotel has good location, but room is pretty old. Traders hotel might be better idea, or if you have a company of 4-6 pax, you might want to consider renting a 2-3br service apartment at Ascott, which located directly opposite Twin Towers.
There are plenty of things to do in Malaysia.
1) KL - You can spend 3d2n there, exploring various places such as Twin Towers, Batu Caves, shopping at Bukit Bintang, try out good local hawker foods at Jalan Alor or Petaling street etc. But do keep in mind that the race will be held at Sepang track, which is 45mins by taxi from city center, and very close to the international airport. Taxi fare there for local cost abt MYR60-80 one way, not sure how much they will charge tourist.
2) You can spend 1 day in Melaka, which is about 1-1.5 hr bus ride from KL. You can do a slow walking day tour in Melaka, exploring various historical sites from Dutch & British occupation.
3) You can explore Genting Highland, which is about 2hrs drive from KL. This is the one of the few places you can enjoy climate of below 20C in Malaysia, and not forgeting only casino in Malaysia. Personally, I didnt like that place as it is very crowded and rowdy.
4) Cameron Highlands - Another below 20C climate highland, but it is more relax and chill. You can either play a round of golf here or experience strawberry picking or tea making.
5) Tamn Negara - If you like nature, do spend a few nights in the Reserve park. You can do trekking and enjoy the nature here.
6) Penang - Populated island which is about 4 hours drive north of KL. It has bets foods in Malaysia, and decent beaches as well (Batu Ferringhi).
Let me know if you need more info.