Carnajo

Will just take a bit longer to heat up
Omni Calculator
Water Heating Calculator
Use the water heating calculator to determine how much time and energy you'll need to increase the temperature of the water.

Would just put a 3kw element in.

From Deepseek :-)
If the voltage supplying your 4kW geyser increases from 230V to 250V, the geyser will indeed use more power. Here's a concise explanation:
Power Calculation: The geyser's power rating of 4kW (4000 watts) is at 230V. Using the formula P=V2RP=RV2, where RR is resistance, we calculate the resistance at 230V as R=23024000≈13.225R=40002302≈13.225 ohms.
Increased Voltage Impact: At 250V, the current becomes I=25013.225≈18.9I=13.225250≈18.9 amps. The new power consumption is P=250×18.9≈4725P=250×18.9≈4725 watts or 4.725kW, an increase of approximately 0.725kW.
Considerations:
Energy Use: The geyser may heat water faster, but total energy over time might remain similar if controlled by a thermostat.
Safety: Operating at a higher voltage than rated can cause overheating, reducing the geyser's lifespan.
Voltage Fluctuations: Consistently high voltage may require a voltage stabilizer to prevent damage.
In conclusion, the increased voltage will make the geyser use more power, potentially leading to faster heating but also safety risks. It's advisable to ensure the geyser is rated for the higher voltage or use protective measures.

I changed my Geyser wise system element to a 2kw, put a geyser blanket on and wrap all the pipes. The heat loss now is minimal - even overnight it drops ±5 degrees max.
Your issue with the over wattage is a question for a decent electrician / plumber.

A 2kw will be enough... it just takes longer to heat the water.

If you install Home Assistant then that will integrate everything into a single app. Google Home / Alexa as well perhaps - I have not looked into it.
No hub needed for Tuya device I linked you to.
 
I specifically wanted something where I could monitor whether the gate was open or closed, the app can also give you pop up notifications each time the gate is opened / closed.

I purchased these for my garage door motors (Centurion RDO) and it works well, can control it via Tuya app and Tuya does integrate into Home Assistant. I do not see why it would not work on a Centurion gate motor.
 
https://www.geewiz.co.za/gate-and-garage-door-automation/161350-smart-wifi-garage-gate-motor-controller-opener-compatible-with-alexa-and-google-home.html
 
There is power required for the device, however there would be 230v for the gate motor as well. What I like about this is that it also is able to confirm whether the gate is open / closed with the contact sensors it comes with. I have set it up so that if my garage doors are left open for more than 5 minutes it must close the doors automatically (incase we press the wrong button at the main gate and open the garage door by mistake).

I use a Sonoff Mini , U need to cut one of the traces on the circuit board so that you don't sent 230V to the gate opener electronics but it is cheap and works well :-=) 
 

I am using a sonoff SV.   It connect to my WIFI. It is powered from the gate motor battery.
I reflashed it with Tasmota and it has been running for months without any issues. I have a Centurion D5 (old model)
I set it up with an integration to my home assistant and have integrated it with telegram.
If I need to let someone in I can simply  send my home a message on telegram and it will open the gate either in pedestrian mode or in normal mode.
The gate also sends me telegram notifications if someone issued a command to open it, that way I can keep tabs on the gate being opened. My cameras also reports any person detected in my yard in the same way. 

@Carnajo Use a Sonoff SV, pretty inexpensive for what you get.
If you want more info, post here or PM me.

@Carnajo the one you mentioned works very well.I have installed mine in the gate electronics enclosure, just ran the 4 wires from my excisting remote receiver the the boar, positive, negative and NO or NC depending on your receiver. Paired to ewe link app. 
 
I sometimes need to open my gate remotely, look at my security cameras and poen the gate all from the office, even open and close the garage and turn alarm on and off

Oh, just make sure you have WIFI at your gate/electronics box.

The G- Ultra is powered by the motor & it's battery & fits within the same enclosure. It uses GSM tech so a sim card with data does all the networking. I have had my Ultra in my D5 for 5 yrs. Still going strong. The Centurion gate main board has pins that the G Ultra integrates with & the entire operation is seemless & there is an app that runs on iOS & Android that allows remote control, gate status as well as allow you to give other users access via their number if they call the GSM unit. 
For tech that was launched 7 yrs ago this device is amazing. 

Has been done with what you suggested provided wifi is available at the motor and for added security a camera facing the gate with remote access (to make sure gate does not stay open or any unlawfull entry).
That's how I have it

Check out HYYP by IDS, if you have their alarm system it allows you to do exactly that, with the app. It connects to the existing wiring to the gate and the alarm panel.