Please keep it simple
Your first recipe should read
4kg Maris Otter
500g Crystal 70
And you have lost me on your hop schedule.
I take it you are going to use
15g EKG @60 mins
15g Challenger @ 10 mins
A good Reverse Osmosis system will remove 99.99% of everything that is not H2O. This is as near to Distilled Water as you can get.
The only problem is, is if you have a very high TDS reading (Total Dissolved Solids) it will still only remove 99.99% of the things that aren`t pure water.
Unless...
If your any good at DIY you can easily make your own filter.
1 x 4ft piece of plastic drain pipe.
1 End blanking piece (drill a small hole 4mm) in the bottom.
3/4 fill with activated carbon pellets. top off with filter floss.
Hose in the top and a gentle trickle through...cleanish water out...
I think you have me wrong. Ive had various RO Systems over the last 20 years. Sometimes its cheaper to replace the whole unit, than it is the various filters/membranes. I was just questioning how low your TDS are before filtration