Her premise and argument is that I could easily lay out $20,000 just to walk in the door and own nothing if I don't find a flat share for at least 6 months first owing to lack of a UK credit history.
* Landlords will ask for extra deposits or multiple months of rent up front on top of deposits
It's usually the case that with no UK credit history, you are likely to have to put down 6 months' rent upfront... so the amount you have to pay depends on the rent. $20,000 sounds extremely excessive though.
Where I live (East Midlands), 6 months rent on a flat would be about £3,000. In London though, the average one-bed flat rents for between £700 and £1,000 per month, so you'd be looking at maybe £4,500-6,000 upfront, or in a flat share, maybe £2,000-3,000 upfront.
* Each utility will also ask for an additional deposit to turn on the service up front
Not heard that before... normally, when you move into a rented flat/house, the utilities will already have been set up for the previous tenant and will already be switched on, so you just have to call the utility company and open a new account in your name, providing the current meter readings.
Things like internet/landline/cable or satellite TV can take longer to set up (2-4 weeks) and if any installations are needed (satellite dish, cables etc.) you may have to pay a one-off set-up/installation fee, but that shouldn't be more than £50-100.
* My renting options will be extremely limited in the first place because I'm an international mover with no history in UK and also because I have a dog
I don't think being international with no UK history will limit your options, but having a dog likely will.
* Even cell phone and internet carriers will ask me for substantial deposits up front owing to lack of UK credit history
Nope - you can just unlock your current US phone and then get a 'pay as you go' SIM for a while until you have built up enough UK credit to get a full contract.
Doesn't have to cost much at all. UK mobile company Three charges £10 per month for 1GB data, 3000 minutes and 3000 texts, or their most expensive pay as you go SIM is £35 per month for Unlimited Data, 3000 minutes and 3000 texts.
* I will, for lack of a better word, be destitute for my first year in the UK while I recover from the costs and start getting my own things no matter where I go - but having a flat share is the least costly way to experience it and permits me to get a credit card or two to charge up and pay off for a year.
I think you will struggle to get a UK credit card with no credit history in the UK, even in a flat share... I'd give it a couple of years of building UK credit before you will qualify for a credit card.
* That I have 4 years tenure with my existing company and can provide decades worth of landlord references will mean nothing in UK to any utility, landlord or agent.
Utility companies won't care less about references - anyone can be added to a utility bill... you just call them and open an account.
Not sure if landlords/agents will consider previous landlord references, since you normally just pay 6 months rent upfront to negate that... but you can ask them - they may consider your references.
So - bluntly - how much of this is genuine and how much is valley of the brides horror story? Are the steps to ensure I'm not spending tens of thousands just to physically move myself and my dog and walk in to a flat with nothing that I actually 'own'?
Most of it sounds incorrect.
You'll probably have to pay a few thousand, but tens of thousands is a gross exaggeration. Your biggest expenditures will likely be 6 months rent for a flat and moving your dog.