You could flash OpenGApps nano over stock ROM, but it made Play services force close.
So, I tried flashing deodexed stock ROM and flashed OpenGApps over it, it worked.
which means it doesn't require a custom ROM.
Since you have Xperia C3 DUAL you should flash this patch after deodex ROM.
To install a custom recovery without having to format your phone you can root using KingRoot and install my modified XZLockedDualRecovery and you can then flash SuperSU through recovery.
Using KingRoot and XZLDR installers requires enabling USB Debugging from developer options.
Sorry can't post more than two links.
For further instructions message me on fb.com/megaahmadf