The Merlin is capable of a high quantity of water, but can also be used for lesser quantity applications like a separate drinking and cooking water faucet. Basically the RO membranes will just live longer if you use it less.
Softened water does have a unique feel to it, but this won't be noticed in your drinking water as the additional filtration process will make it very normal. Here is a link to some information concerning the issue of Sodium in your softened water.
Water Softening and Sodium, comparison of sodium levels in food and softened water RO will remove over 95% of the added sodium, so with an RO system your drinking and cooking water will be isolated from the sodium issue. Other filtration methods are incapable of removing the sodium, and frankly with water as hard as yours, I don't know how you can avoid using a softener. I have softener filters, but you would go through them so fast it simply would not be economical.
For your situation I would recommend a sediment filter to 5 microns pre-softener followed by a softener, then a carbon filter to help normalize the water from the softening process, and at the kitchen tap an RO system through an isolated faucet. This will fix all your water problems for the whole house.
Please feel free to ask more questions, that's why we're here.
Thank you,
WaterFilters.NET