I would suggest 9mm for its very similar performance with premium ammo, higher capacity, and cheaper practice. .40 Short and Weak is a piss poor excuse for a 10mm substitute. Not that it won't work, but it provides no significant advantages over 9mm which I am aware of.
About night sights, let me first explain that in a defensive shooting at typical civilian close quarters distances, the sights are almost never going to be something which is used. Unless you are EXTREMELY well practiced, your body won't allow it, and you'll instinctively fall back on point shooting because it's faster and your mind will be focused on your assailant, not your sights. If you don't practice live fire at least several times a month with at the very least several more dry fire practice sessions, forget the sights up close.
If the average person isn't likely to use sights in the day time, imagine how much less likely sight use is in the dark. This is the key reason why night sights aren't likely to help you. HOWEVER, I can't and won't knock them if it's something you're interested enough to get. The thing I don't recommend is any style other than XS Express night sights. They combine very good usable precision with extreme speed, relative to most of the rest of what's out there. The only thing better is laser sights. I don't know of many models which have them as OEM, so if you want them I suggest adding them later.