You are getting a really good deal atm for a limited edition model. Tax etc depends on if dealer had added to his quote as you need to check the breakdown. But principally you are right, the dealer pays DVLA not you for year 1.
When I bought my car a few years back, I got quotes through brokers and printed them out, took them into the dealer and said I'd buy from them if they price-matched. The quotes you'll get through a broker come from other Toyota dealerships, so are a good indication of what discount is available.
You may find that the Blue isn't on the broker sites yet, but they may have the orange (the previous limited edition), which was a similar price as far as I remember.
My gut feeling is that the price you're being offered is pretty competitive, but the broker quotes are no-obligation so make your dealer wait while you check it. It's worth trying a few brokers - Carwow, Drivethedeal, and Broadspeed are the first three that spring to mind.
I ordered a Celica via one of these price saving brokers. Unless it's already coming from stock in production (which given the small run will be unlikely) it is basically treated as a one off order on the production line which can take in excess of 20weeks.
Guess what they screwed up my order and I actually ending up waiting 9months. Still the extra waiting meant I had saved practically all the money needed to purchase it lol
I had a 4 month wait for mine back in 2015 due to the changeover of model year; back then it was to make the engine Euro 6 compliant. I wonder if they're in the same situation again, and needed to stop production to engineer in a particulate filter?
The WLTP I believe is on production cars manufactured after Sept 2018. Although the legislation came in Sept 2017 wonder if you can order just before and get a car made without a Particulate filter. It must restrict performance even further on our cars.
Interestingly VW appear to have scraped the GTi (without the performance pack) as it now doesn't meet the new regs and many are dropping manuals in favour of the small MPG gain with DSG. According to VW website only the Up, Toureg and T-Roc meet it at the present time so not long left. It must be a nightmare to find a work around/cheat with particulate filters and fuel maps.
Assuming that's the issue, I would expect they've allocated all the pre-WLTP build slots already and have started filling the WLTP-compliant build slots - and I would not be surprised by delivery dates in January/February. They might have pioneered Just In Time manufacturing but that's cutting it pretty fine for compliance...
If you wanted a pre-WLTP car it might mean just taking whatever spec Toyota have in stock in the UK; they may not have too many lying around other than ex-demo cars.