that guide doesn't mention wiping data and i vaguely recall people do that when flashing roms, should i do something like that?
Many times developers don't specifically state that you must wipe data, but the fact that not doing so generally gives rise to so many errors, that I'm surprised people still "dirty flash" and complain about errors.
On the other hand, if clearing data for the play store/google framework/etc. didn't work as
@matt4321 suggested, and you are still can't access the play store after flashing an FTF (and having wiped /data, obviously), then it's most likely a problem with the GAPPS that come with your FTF/ROM that you flashed (unlikely), or a problem with your internet connection.
If you have any .apk file you wish to install, and you have ADB installed on your computer, just enable USB debugging in developer settings, connect USB cable, connect to your phone through ADB (adb -d shell) and type:
Code:
cd /storage/sdcard0 (or sdcard1, or wherever your .apk file is located)
pm install name-of-your-apk.apk
Something which can also be done with a terminal emulator, which I doubt you have since you don't have access to the Play Store.