Yes, you'll want a heat lamp on them even though they are inside. And leave it on 24/7.
Rule of thumb is to start at 95 degrees the first week and lower the temp by 5 degree each week until they are to about 70 degrees. Some chicks will move faster to less heat, some slower. I like to put the lamp at one end of my brooder and their food and water sort of in the middle. This gives them a cooler end they can escape to if they need to. It's also a good set up to be able to tell if you need to drop the temp faster or slower for your chicks.
I personally wouldn't keep them in a cardboard box the entire time. Not only will it get extremely flimsy as it gets wet, it will also absorb the odor. They (typically, again just rule of thumb type thing) need to stay in the brooder until fully feathered, for most breeds this is around 6 weeks. But the actual feathering and not age needs to be taken into consideration. But, 6 weeks with any amount of chickens will put a cardboard box through all it can handle, and then more. Most definitely build them a brooder. Doesn't need to be anything fancy. I have two - one that they can stay in for the first week or two, with really nothing in it other than the lamp, food and water. Then we have a larger one for as they outgrow they "baby chick" stage and start becoming curious wanting to explore and have fun. It has small starter roosts in it, a swing, a couple boxes for them to crawl in and around and several ledges for them. Both are made out of toy boxes my father made for my kids when they were young (they're huge lol). I just replaced lids on them with screen and outfitted the inside of the largest one with all the fun stuff.
As for bedding/litter; nothing cedar - anything else you might want to use is pretty much ok. I use paper or paper towels for their time in the smaller brooder (1-2 weeks) and once they move I've used everything from sand, to shavings, to leaves, pine straw and hay. Hay or shavings is what I would recommend. Sand is much easier than anything else to clean out, but my brooders are in the house and that makes a big, big mess as they start getting older.