Continue to feed, slowly. You can winter a colony on one Warré box. No worries. And no need to combine at this stage.
In September/October you do the following setup.
Put two sticks on top of the topbars of the uppermost box.
Take a fondant package, cut a square into the underside and put that on top of the topbars. Cover the whole lot with an empty hive box and fill the box with insulation. Keeping the warmth is very important.
The winter cluster of bees will be right underneath the fondant package. The bees eat their way right up into the package. First you see them eating through just a small hole.
It is very important to leave the plastic on the fondant, so the warmth get trapped in the foil and with it the humidity that condensates on the plastic foil. See picture. This way bees have both, food and water in winter. Plus the warmth is trapped in the bag, so they stay warm even in a smaller cluster.
Bees eating their way up into the fondant...
Bees walk from the comb straight into the bag. Usually a good portion of the bee cluster sits in the bag later.
This way you can overwinter even smaller colonies in a Warré hive one a single box. In Spring they simply explode and make nice colonies later.
It was too late to start a new colony, the earlier you start them, the less trouble you get. Of course.
In winter check regularily the fondant - once it is eaten up, replace it on a sunny day (flying weather would be best) with a fresh bag of fondant.