Your basic idea is a very reasonable one and many have endeavored to come up with a set of water 'recipes' over the years, including me. Just for laughs, here's mine for Munich from way back when:
Target City: Munich2 Base Water: Deionized
Balancing pH 9.8255 is greater than 8.40 and is thus set to 8.40
Net charge (imbalance) at this pH: 0.9102 mEq/L
SALTS ADDED FOR THIS SYNTHESIS:
Sodium Chloride : 1.37 mg/L
Calcium Sulfate Dihydrate : 15.22 mg/L
Calcium Chloride Dihydrate : 76.56 mg/L
Magnesium Sulfate Heptahydrate : 197.94 mg/L
Calcium Carbonate : 161.21 mg/L
Magnesium Carbonate : 0.00 mg/L
Sodium Bicarbonate : 5.32 mg/L
Carbonic Acid : 3.16 mEq/L
You can see this recipe and the others at http://www.wetnewf.org/pdfs/Brewing_...es/Recipes.pdf
. They were generated so long ago that they were done, not by a handy spreadsheet as we do today, but by FORTRAN code that ran overnight to produce these 21 recipes.
Since those days perspectives have changed and the idea of following a recipe has fallen into disfavor for reasons, some of which, have been aluded to in earlier posts. One is the problem with chalk. If you look at my Munich recipe you will see that chalk is listed and that is because carbonaceous waters come about through the dissolving of limestone by carbonic acid. If you want to emulate carbonaceous waters you must use carbonic acid. Just adding chalk is half the process. You cannot closely duplicate a carbonaceous water without the CO2.
Without going into all the other problems with profiles (one of which is that most of the profiles in the literature are not valid because they cannot balance electrically unless the pH is unreasonably high, IOW, they tend to understate the alkalinity) I will mention that even if you do correctly implement one by the use of CO2, a laborious process (but nature takes even longer) most of the chalk/CO2 will come right out of solution as soon as the water is heated in the HLT and all your trouble will have been wasted.
We treat water for two reasons. First, is to establish proper mash pH. This must be done whatever type of beer we are brewing. Getting rid of alkalinity is the key to proper mash pH thus any profile that calls for addition of carbonate or bicarbonate is suspect. The exception is beers that use a lot of dark crystal or roast malts. These contribute acid which can drive pH too low and in those cases alkalinity is needed to neutralize that acid. If a beer requires alkalinity then it probably has too much dark malt. This comment needs to be clearly marked as opinion as home brewers love to experiment and may well wish to brew beers with 'too much' dark malt in them. In these cases sodium bicarbonate can be used in the water up to the point where the sodium becomes annoying or lime (calcium hydroxide) can be used in the mash. Chalk should be avoided for rather complex reasons but they are set out at http://www.wetnewf.org/pdfs/chalk.html
if you are interested.
The other reason for treating brewing water is to make sure that it has appropriate levels of chloride for the desired body/mellowness and appropriate level of sulfate for hops harshness/dryness.
The question then is how does one proceed given that he wants to brew a Munich Helles? Rather than try to recreate the water of the ISAR or the sources used by the modern city of Munich he should realize that light beer cannot be brewed with carbonaceous water and that absent the hardness and bicarbonate Munich water is pretty soft and low in sulfate and chloride. Starting with low mineral water such as RO or Portland water a modest addition of calcium chloride should be all that is necessary. The fact that Munich water contains some magnesium does not mean that you want magnesium in your Munich style beer.
By contrast, if you are going to brew a Burton style ale you need to understand that a lot of Burton brewries' waters were highly gypseous and add some calcium sulfate in addition to the calcium chloride. This is a good place to caution against cleaving to the chloride to sulfate ratio as a parameter whose value must be closely maintained for a particular beer to be any good. The correct amounts of chloride and sulfate are those that give you the beer you want. This must be determined by experiment. You can use published profiles to give you an idea as to what those levels may be the first time you brew a particular style and you can experiment with adding gypsum and calcium chloride to finished beer to see what their flavor effects are.
I could go on but all this stuff has been hashed over thoroughly here and elsewhere in the home brewing 'literature'.