I was able to install 5.0.2 using flashtool, but because I can't get into recovery, I can't flash this prerooted zip file.
I'm a bit of a noob in regards to Sony devices, but is it possible to flash this file using flashtool..?
Simple answer....no
The recoveries were really only working properly on 4.4.4, and that was only if you unlocked your bootloader and flashed a dual recovery+boot.img. For some reason, flashing a recovery to the normal "recovery" partition, even though successfully flashed, wouldn't allow access to it. Only the "FotaKernel" flashing (dual recovery) was working somewhat.
Theoretically, under 4.4.4, you could get to recovery by using "fastboot boot recovery.img", but it was ify-ify if the recovery would show on the display. I had to do it numerous times.
Once you've upgraded to 5.0.2, the only option is
a. Wait for a dev to make a compatible recovery (probably fotakernel type, or one that can be booted using "fastboot boot recovery.img"
b. Wait for somebody to create a modified boot.img which will allow adb push (to push superSu using up to date binary). I can do this, but right now am busy at work, and won't get around to doing it until sometime this weekend.
Either way, I suspect it's going to require an unlocked bootloader. But I wouldn't reccommend that until you learn the disadvantages and back up your DRM keys.
You could probably roll back a couple versions to an earlier OS (ftf flashing) and try with what recoveries we have now.
I'm still on 4.4.4 (unlocked bootloader and backed up DRM keys, not that you really need them for most folks), so will be working on it this weekend.