Just open the "Samsung Cloud" app, tap on three vertical dots > "Settings", and then disable the "Sync and backup while roaming" option, and you are good to go.
I am an S10+ user too, but I have never faced with the problems you've mentioned here. Depending on your RAM, these tips may help you. Try to avoid keeping a lot of apps open on the background. Restart your smartphone at least one time in a day (usua...
As far as I know, for connecting to the electronic devices in your home. you need to buy Samsung's SmartThings Hub, which is around 90€. With that you can control all devices which are connected to the smart adapters.