I’ve read that when knitting tops that it is better to use 24" long needles. However, 24" needles are circular needles.
Is it better to knit tops using circular needles? (Even if the pattern doesn’t call for circular needles)?

What would be a good length to use for knitting tops on regular single point needles?

Circular are more versatile, so I find them a lot better to have than a whole set of others. All you need are long circs and you can do anything you want, including socks, fingers on gloves, sweaters, afghans.

Circs are easier to use for sweaters because you don’t have all that weight hanging off the one needle, and making your arms sore. You can do flat or round knitting with circs… there is no law saying you MUST only do circular knitting with circs! Knitting is just working one stitch at a time with two pointed sticks. What they have in the middle doesn’t matter.

http://www.youtube.com/watch?v=C-aWWES8Rxc

Let’s say a scarf that is 4 feet long. I just took up knitting and I’m wonering how many rows I’ll have to knit.

Thanks in advance!

You could measure your scarf when you reach 12 inches. Then count the number of rows it took to get that far.
Take that number and times it by 4.
That amount should be the total number of rows it will take you to get to 4 feet.