The bought queen will be walking round checking things out. I am an expert on weak hives. I nearly lost 2 hives after I introduced lovely golden bought queens. The fairly strong hives just got weaker and weaker. One finally lost the queen and was replaced by a laying worker, so that hive died. The other was only saved by finally superceding itself and the daughter is a beauty. It is now a strong hive. I tried everything to stimulate laying - feeding, moving to a better place, adding more brood. A weak hive goes in circles for a bit..not enough bees to bring in supplies and so maybe the queen won't produce enough brood so there are enough bees. You have to get over a certain number of bees usually for things to go ahead. But don't worry! You saw a queen. That is the main thing. I've tried to requeen and it hasn't taken, and then I also have a hard time spotting queens, so your hive is halfway there. I think Michael Bush said it can take a couple of weeks for an introduced queen to lay. If she is a dud, then she won't lay much no matter whether you are feeding or not. But when she starts and you see a heap of eggs at one time, then maybe you will be adding 3 or 4 supers before you know it. I really question whether you need to feed. You are in a good area and it is spring, so they should have no trouble finding their own. I'd probably just check every so often to make sure they have some honey and are not starving. Also, keep the space down to the smallest required. Another thing I learnt from bitter experience is that a weak hive takes longer to recover from inspections, and you have to weigh up whether you are setting them back with frequent inspections but also knowing problems when they arise. You can tell a lot from the outside of the hive too. You don't want to be inviting SHB with pollen patties either. You are correct that normally you add a frame or so of brood to a split, and this helps keep the numbers up. If things get dire, maybe recombine the 2 hives...but I think you will be all right in a few days when the queen gets going. Don't worry they haven't drawn out the plain foundation. They don't need that space yet and need those resources and beepower for other things.
I'm not quite sure either why you destroyed queen cells after a swarming, unless this was on the half you added the bought queen to. If it was on the original hive you might have lost them a chance of replacing the old queen.
Sorry this is so rambling. Thanks for all the updates. You will be fine once you get those 10 swarm calls in a week and the bees draw out a super in no time.