Add the metering plugs to Z2M. At the very least, it’ll allow you to configure reporting for your chatty plugs.
It won’t prevent your zigbee network being spammed, but at least it will only send out mqtt messages at the frequency you describe.
Yes, as long as you’re using entities instead of devices in your automations, you should do this.
Get a coordinator which supports LAN or PoE and avoid the hassle of dealing with USB-only coordinators. You’ll be able to place it anywhere central in the house which has access to ethernet & 5v from a phone charger (if you’re not using PoE). Pick a coordinator with an external antenna.
Hell, if you’re not totally sure you want to keep the SkyConnect, get a coordinator which has 2 zigbee radios, like the Sonoff dongle Max or the SMlight MR range. It’ll allow you to run ZHA & Z2M on a single coordinator if you change your mind later on. Bonus points: If you end up falling in love with Z2M, you can run 2 separate instances of Z2M on it - 1 for your metering plugs and the other for the rest.