I have two computers, one i built for gaming and then an old laptop that I use mostly for just word-processing and programming. I don't really use my laptop for gaming at all as I found i was unable to run anything released in the last year or two (or in 3d for that matter). However, I had heard sins ran pretty well on old hardware so I decided to give it a go and found that low and behold the old compy could run it on low settings. So like he said above they have done a great job with the graphics scaling and you really shouldn't have a problem running it. 

In regards to heat, sins is like any other game and is gonna generate a pretty good bit of it. I would advise you just to make sure that whenever your playing to have your laptop on a hard surface where the fans can circulate the air well. As long as your on a hard surface it should be able to keep itself cool enough. Other than that enjoy the game and I wouldn't worry too much. I've been terrible to my laptop and even had it hit the heat threshold once which caused it to do an emergency shut down to try to save itself. After letting it cool down it ran fine the next boot (though I wouldn't recommend ever having this happen ^^).

I use speedfan to keep my temp on the desktop and monitor cpu usage. I would not recommend to much time operating past 65c on the cpu or gpu. At about 68c - 70c my fan rpm almost triples notifying me of high heat but that's already going to hot to long for me.

Playing a laptop on the bed using the blanket or a pillow is sure quick death for any laptop.