Planning the move, it's intimidating, how do you time it all?

My first step is getting registered with my professional title for my radiography job, then looking for work which seems plentiful for my profession.
I'm wondering about all the rest; we'll have to get rid of most of our things, sell the cars & the house, get things shipped, get the cats over, find a place to live, and somewhere in this timeframe I'll have to stop working in Cali and start working in England.
How does all this go down?

It can be done many different ways. I had 6 months notice that I was moving which was helpful. Job was sorted in June and I moved at the start of the year.

Beat option would be to accept a job who doesn’t need you for a few months. Three to six month notice periods are common here, so you wouldn’t be limiting yourself saying you need that much notice before beginning.  That will then ensure you have a job before selling everything you own.

I’d recommend NOT selling large items (house/cars) until you’ve secured work and signed a contract as selling those quickly is just too risky.  For example, I didn’t list my car for sale until a week before I moved.  I hired a car for my last 2 days in the USA.

The second option (if the long notice period is still too quick of a turnaround) is for your partner to stay in the USA while tying up loose ends before joining you. 

My first step is getting registered with my professional title for my radiography job, then looking for work which seems plentiful for my profession.
I'm wondering about all the rest; we'll have to get rid of most of our things, sell the cars & the house, get things shipped, get the cats over, find a place to live, and somewhere in this timeframe I'll have to stop working in Cali and start working in England.
How does all this go down?

I'd start by researching moving your cats. We did it years ago so I'm not up to date on the current rules but I'm sure there will still be a time dependent element and a correct sequence of events. At the time we did it it was microchip, rabies vaccine, waiting period, vet check, paperwork.
That way you won't be held up by that.

I'm hoping that the health board which sponsors you for your work visa will also arrange for the HPC registration. I don't know what's involved but I'm sure it'll be a pita to try to do it yourself.
https://www.hcpc-uk.org/registration/getting-on-the-register/international-applications/

You might find that the health board will also be able to house you at first while you look for a place.

I sold the good car to Carmax, it was so much easier than dealing with the tyre kickers.  I organised the shipper and just kept putting the date back until we had the visa/flights etc.

We didn't need visas or a job as we were retired. Our son moved the following year and first lived in our house for 3 months while he looked for a job (took 6 weeks), and to buy a house which took 3 months.

Our process was to sell the house in the USA first and move into an apartment.  That in itself got rid of a lot of excess furniture and junk.

Once we had a rental house in England to move to we sold or gave away a bunch of stuff and looked for an overseas carrier to move the rest.

We sold the car to Carmax after picking up a rental for a few days.

Once the moving company loaded all our gear and left we moved into a hotel for a few days before flying home, dropping off the car at the airport.

No pets

Our son had me to help. I flew over for a couple of weeks before his flight out to help him pack up and move from his rental apartment (he had never owned a house). We only stayed in a hotel for a couple of nights before the flight was due.  He sold his car to a local dealer after getting a quote from Carmax. He left his job in the USA just days before we flew out.