Ok first things first. You can give grain to your buck. In fact most pack goat owners feed a grass hay and supplement a grain. Usually a 14% all stock or even goat chow for those that can afford it. This is done because alfalfa has a 1.50% calicum by volume level on average. Grasses are lucky to get to .50. Wethers are much more acceptable to UC so a more cautious feeding method is used. So depending upon what you are feeding him, give grain as needed. Bucks for the most part dont have issues eating just alfalfa and nothing else. We have feed dairy quality alfalfa for nearly 20 years (no grain supplement) and have never had a UC issue to this day. And as for areas with higher calcium soils, that doesnt really translate into a crop grown feed. There are lots of variables but there is only so much a crop can absorb and the longer that ground has been farmed the less minerals it has to pass on to a crop.
A loose grain mineral supplement (not blocks), given free choice is of course needed. Most blocks are to hard and a goat can wear down their teeth trying to get what they need outta it. Dont use a sheep and goat mix as the amount of copper a sheep can have is way lower then a goat should have. Use a cow mix. If you can get it as a pre mix the mineral contents will be higher. Cow farmers then add salt to the pre mix. DO NOT DO THIS for goats. The pre mix has enough salt in it already for goats.
And no on the baking soda for boys. For reasons already mentioned but I wouldnt even give it free choice to does either. Its a rumin buffer (meaning it helps it) there is no need for it to be given if everything is in working order. If you want, give a half cup in your grain supplement. Do not add it to loose mineral mixes. Some goats will eat more of the minerals then needed just to get to the baking soda.