hey there
yay another aussie here
with getting a Tacho into your Gen3, its really hard to tell if you can do that or not.....
your best bet is to take apart the dash and take a look behind the cluster, and see if you have an extra plug....
i had a Gen3 like your one, but it was the CSi model, so it had the Tacho already

that type of gauge had 4 plugs (fuel, temp, tacho, speed), for your one, there might only be 3 plugs (fuel, temp, speed), so you can hope there is a spare one sitting there for the Tacho
i pretty much took apart my Gen3 when i had it, so i found out what wiring was present and what wasnt......
in the way of accessories, im pretty sure for your model, you will have wiring for a Digital Clock and Glove Box Light. I found these both out and they were both plug and play
good luck with everything