Wow, that's a shower head and a half! I don't know of any formula for deciding on pump pressure/flow rate, but for that head I would go large!
I've installed two Salamander RSP 75s 2.25 bar (at my old house and new house) both with Mira Gem 88 valves. I used the standard Mira head on the first one and the shower was excellent but I was worried about it emptying the cold tank so I put the supplied flow restrictor in the valve which still gave a good shower but I'd probably wasted money on that size of pump.
With the second one, I had a bigger CW tank so I used the same pump and a high flow head. This gives a good shower with loads of flow but the pressure is OK but not startling.
For your head I would go for a minimum of 2 bar, possibly 3 bar.
You don't need a thermostatic valve if you have dedicated feeds from your essex flange and the cold tank but if you've already got it, it won't do any harm.
Now that you've got pipe benders put in as many bends as possible instead of elbows, this keeps flow up and noise down.
Also, make sure you use a high flow waste in your shower tray to make sure it can keep up and not overflow the tray.
Having recently done the two "decent" showers I've learnt a lot about them so ask away if you've any other queries. There's loads of info in these pump instation instructions that I used:
http://www.salamanderpumps.co.uk/Download/instructions.pdf
By the way, I'm not aware of any "good" pumps that are variable so I would approach these with a bit of caution. Stuart Turner seem to be commonly recomended.
Hope that helps.