A larger softener is not a problem for a regular household application. I would recommend sizing it to regenerate at least every 15 days, anything beyond that is not a problem, just not necessary.
The debate about drinking softened water is extremely complex, but for the most part, you will be fine unless you are on an extremely sodium restricted diet, or if your water is very hard. (over 50 grains). The WHO recommends against drinking softened water but that is more for third world country issues of health due to the lack of nutrition in the diet more so then the concerns for drinking water with slightly elevated levels of sodium. Calcium and magnesium deficiencies are common in some countries, even the trace amounts found in water can be beneficial when the body rarely sees other sources.
For residential applications in "normal" size houses, try to keep the softener tank size 14" or less in diameter due to lower flow channelling issues.
Hope this is helpful.