I think it depends on the device. My understanding is that routers will find their own connections, so adding them through the co-ordinator is fine as that will change over time. End devices may stay where you put them, unless the parent router becomes unavailable - I have read that this varies with the manufacturer - so it may be worth adding them via the nearest router with a strong signal.
One thing that affects network performance is the proportion of routers to end devices - you don’t say how many of each you have. There isn’t a magic ratio - it will depend on your home and the devices you have (lightbulbs are not necessarily the best routers), but it may be worth adding a “repeater” router in each room - that is, a router that doesn’t do anything else.
I assume that you already have your SkyConnect on a USB extension cable to avoid interference. A longer one than the one in the box doesn’t do any harm - mine’s 2m.
I wouldn’t be in too much of a hurry to change channels. Some people report good results, but it isn’t a magic bullet, and you have to re-pair all the devices, which is a pain. You also need to be aware that zigbee channels are not the same as wi-fi channels. There’s a post about it here.
The trouble is, a hub like Philips Hue has a much bigger antenna than your SkyConnect. You need to build a stronger network to compensate. “Rock solid” takes a while to achieve, and it isn’t entirely under your control - the network has a life of its own.
I assume you’ve looked at this: