You need scatter file to use spflashtool. Try MTK Droid tool to create one. You could do it since your phone is rooted. If you have twrp back up, then just do a restore. You do not have to do anything. When you do a restore, twrp does everything. After restore, do wipe cache and dalvic. If you are going to flash stock rom using twrp, factory reset the phone, but do a back up before factory reset. On twrp click install and it should give you a choice from internal or external. From there just pick your rom. Do google search: how to create scatter file using MTK Droid Tool, how to flash rom using spflash tool, how to restore using twrp recovery, how to flash stock rom using twrp recovery.
Good Luck keep me updated.