Split power at gate for other items- add light and WiFi unit

Depending on how your cable is connected.

if it were rcd protected I would disconnect the cable at the gate end and connect it to an outside twin socket

id then use a plug and lead to feed your gates.

and another plug and lead to feed a waterproof enclosure with a twin socket inside that feeds your additional equipment

Brilliant. Then it’s dedicated circuit with rcd protection . I’d do it the way I proposed so.

An outdoor socket may not work depending on what you're plugging into it. E.g. if that TP-Link has a power adapter plug, you won't be able to close the socket's water-resistant lid. Same for the USB.

Assuming that's the case, you can purchase a plastic box on Amazon to house an extension lead and plug things into it, designed for Christmas lights but works for anything. What I'd do is connect the existing SWA cable into an outdoor junction box, and then disconnect the plug of a standard extension lead, and connect the extension leads wire into that junction box. Then you can use a bit of 1.5mm 3-core flex to connect between the gates and then put a plug on it and plug it in. Or, connect that flex into the junction box. In regards to removing the plug of the extension lead, it goes back to the switched fuse spur so it'll be fused there.

Then you can put a plug on your LED lights and WiFi access point into that. Since you're going to have WiFi at the gate, you could use a smart plug to control the lights. Or you could add a photocell to the lights so they come on at night automatically, Knightsbridge do a good one that has a timer function so once it goes dark, it keeps the lights on for 2hrs, 4hrs, 6hrs etc.

But to answer your questions about that setup suggested by meercat, you don't seem to be missing anything. A simple plug with a 13amp fuse and a 1.5mm flex is all you need to connect the gates, 1.5mm is good for up to 16amps/1920w, and from what I can see, electric gates use around 700w when operating.

They're very useful imo, I have them in use for garden spike GU10 lights, and I use them for christmas lights too. Used to have to put 2 bags around an extension reel, not the best solution!