Hmmmm........to be frank, no, Yamaha 15W isn't the amp of choice, are u looking at amps that already have efx built in or those which are basic bcos u already have pedals or other efx?
As for the guitar, for $700, u have a wide range of choices. Cort, Ibanez, Tokai, Edwards or perhaps a 2nd hand PRS come to mind. Alternatively, get a cheaper guitar like Timbre or Smash and upgrade the pickups. Depends on tonal preferences, Ibanez RG series have darker tones meant for metal-type songs, while Tokai, Edwards LPs have that fat midrange for rock, PRS is more balanced. There are of course, exceptions but go try out stuff first before buying. Cheerz!