I used the bag from the get-go, without any sort of leather care products whatsoever, and it seems to hold up well. There aren't any noticeable scuffs or scratches so far. Unfortunately, accidents do happen, and sooner or later the leather will likely get a little scuffed, but it seems to be holding up well.
I use this bag during weekend trips and occasionally as a gym bag, but at the end of the day, treat it as a leather product and it should last you (don't toss it onto a gravel sidewalk or running track and there shouldn't be a problem at all).
As far as water resistance goes, it's porous, and not suitable or pre-treated for heavy downpours, so if the bag gets wet, dry it off as soon as possible. Light drizzles are fine--there may be patches here and there, but it disappears after it has evaporated. If you wish, I suppose you could use some spray-on waterproofing, but I haven't tried that.