Pretty much all hotels in Vegas you can cancel with no penalties if you give them 48-72 hours notice before check in. So if you find a deal on a hotel, you can book it but then if you find a better deal, you can cancel the first hotel.
Package deals can be cheaper but you can lose a lot of flexibility on flights and hotel rooms. For example, say you want to take the red eye home and get a corner suite, you not likely to find a package for that. Booking separately give you more options.
Its also a good idea to setup a google flights alert which will email you when flight prices go up or down.