You can’t use the Sengled gateway if you are also using the smartthings hub. It’s one or the other.
As far as a good zigbee repeater, right now I am recommending the IKEA Tradfri. It’s just a simple single socket on/off device, but it’s a good Zigbee repeater and better than most if you want to also use the inexpensive Xioami sensors. And at a price of less than $10, it’s hard to beat. The bulbs and the plug-in pocket socket work well with SmartThings. There is only partial integration with the handheld buttons and remotes, so I would skip those for now.
The bulbs and the plug-in pocket socket work well with SmartThings. There is only partial integration with the handheld buttons and remotes, so I would skip those for now.