newby question about sore seat bones and saddle bags

[OakLeaf]

What Eden said.

As far as saddlebags ... I think it would depend on the size of the bags, and in any case it might have to be a permanent conversion, just because a horse's back is a whole lot wider than a rear rack on a bicycle. The bottom of the bag needs to be higher than the rear derailleur. Also, for saddlebags, you want to make sure you have a rack with plenty of side coverage to keep the bags out of the spokes.

Weight carried low is always going to affect your balance less than weight carried high, so yeah, while some people can ride comfortably with backpacks on, they're not really a good choice for loaded touring or heavy shopping. As far as the weight of the bags - that's entirely up to you, just keep in mind that everyone has a range of weight that's comfortable and safe for them on any particular bike, and the more of that is luggage, the less weight you have left over for "stuff."