Glad to hear you've succumbed :thumb:
That calculator for the Invert Syrup is a gem, what I did was pour the Golden Syrup into a 1 litre measuring jug on the scales, pour out what I needed and then sit it in a bowl of just boiled water from the kettle, allow a few minutes to heat up then pop back on the scales and add the molasses to the ratio required, then 5 minutes before it was needed, add 750ml of wort to it and mix it in then pour into the copper.
I added mine at 15 minutes from the end.
Essex Yeast is only available January and February of the year but a good solid liquid substitute is WLP002/005 and Wyeast 1335.
As for dry I doubt you will find one similar but your best bet is a dark ale yeast, it's main trick is to accentuate the malt aroma but the hop flavour.
Works really well all of their beers.
As for the Brewers Caramel is isn't a compulsory ingredient to do the beer, it is purely a colouring agent. If you aren't fussy then you can leave it out, it is however, available from Hop & Grape in a 250ml Bottle. Bout 7 - 8 pound if I remember correctly.
Hope this helps.
Cheers.