1) they say you should clean your tack after every ride, but I don't know that many people who do that! I usually clean my tack before every show (which is almost every week during the spring-fall).
2) Saddles DO mold/mildew if they don't get cleaned often enough! Especially if it's humid where you live. Whitish greenish fuzzy spots? A simple saddle soap gets that right off. And that's usually a good sign that you might want to clean your tack more often.
3) it's normal to add holes to bridles to help them fit better, as long as it's just 1 or 2 and don't affect the placement of the straps. Do you have a leather punch? They make it easy to get a small perfectly sized/shaped hole that doesn't stand out.