Upgrading from v1->v3 tado

I've had a v1 (Connector kit) tado for a few years now, but it has stopped working - the remote temperature sensor unit has stopped working, and I can't get it going again. Additionally, I wanted to add some tado thermostatic valves, which require a newer version of the tado base unit. Up to now my tado has been controlling both the central heating and hot water, which I want to contuinue doing.

My current set up has the "smart thermostat" box mounted in the airing cupboard, basically replacing the old HW/CH controller (and plugging straight into the old connector, which I assume is a fairly standard connector allowing different controllers to just plug & play). The bridge unit plugs into my internet hub, and the remote temperature sensor was in our living room, and connected wirelessly so had no physical connection.

I've upgraded to the V3+ app on my tado account (this was a one-off payment as an owner of an original v1 system).

I've purchased a V3+ starter kit (with the smart thermostat), the tado extension kit (which allows me to control hot water), and a few thermostatic radiator valves.

What I'm after is a bit of guidance on how I install all this, replacing my existing kit. It's important that I use my existing account, rather than set up a new account, too. Any hints/tips on what I need to do, and how much I can just follow the "automatic" instructions that I'll get, and if there's anything special I need to do as an upgrader rather than fresh install?

TIA

Paul.