From the way this question is phrased you either spent a lot of time reading up on Rhinoplasty surgery OR you must be in the medical field.
What techniques are used to slightly decrease bridge height/width of the nasal bony pyramid? - Rhinoplasty should be done incrementally but WHAT is done depends on your complete presentation and cosmetic goals. While the dorsum can be lower minimally with some rasping, a real narrowing of the nasal pyramid would require in-fracturing.
Could the surgeon be over aggressive and make it too narrow? - Poor results can be achieved in Rhinoplasty. Pick your surgeon carefully and make sure he fully understands what you want done.
I'd also like to increase my Nasolabial angle a little, would it be simple enough to just shorten the caudal part of the septum and barely overlap the lower lateral cartilages? - This can be done in several ways, from repositioning and upward rotation of the tip complex, to, as you suggested, shortening the caudal septum and reducing columellar show.
Again - pick a Plastic surgeon who shares and understands your cosmetic goals.
Dr. P. Aldea