Quick question about bottle carbing my cider

I'm ready to bottle the cider I started 3-4 months ago and have a couple of questions about bottle carbing. I was planning on using table sugar, but had another idea. I have two more gallons of juice in 1 gallon carboys that I am going to start right now and thought it might be possible to use some of the unfermented juice since I need to make a little room in the carboy anyway. Is this possible and any idea how much I should use? Secondly, I put the current batch in the fridge for a week or so to cold crash. Will I have enough yeast in suspension or should I try to get a little up off of the bottom? Thanks for the help.

Yes, take a gravity reading and divide the points by 4. This gives you a Brix reading, which is grams of sugar per 100 ml. 1.060 -> 15 Brix -> 15 gm/100ml ~> 1 oz per cup.

No problem with the yeast.

Thanks for the help, I'm looking forward to tasting this in a few weeks.