Depending, of course, on your grist, the advice to add alkalinity is probably not sound. Assuming 80% base malt with a DI pH of 5.6, 10% of something like a Vienna and 10% Caramel 60L your mash pH, with the calcium, will be right around 5.4. If you add modest amounts of alkali you can raise that to 5.5 or so without detriment. The danger is that if your base malt DI pH is higher than 5.6 (and for most malts it is) or if your darker malts are in smaller proportion, or of lighter color or of greater DI mash pH, then your mash pH will go up too. If, for example, your base malt DI pH were 5.8 your mash pH would go up to about 5.5. That's OK but if you added alkali then you would be pushing it up even higher and now you are getting out of the region you want to be in.
Best, of course, to obtain a pH meter and know rather than guessing based on assumptions.
Unless there is some special reason for wanting to have this mineral profile (which I would think to be quite crunchy) I would start out with a half tsp of gypsum and a half tsp of calcium chloride per 5 gal treated and go from there. See the Primer (it recommends more but I really feel it is better to start out low and work your way up as less minerals generally make better beer).