[Q] Difference between 16 and 32 gb

Hi there!

Just got myself a "LG G3 Gold 16gb" in mint condition. It´s just been rooted by me and I´m about to install TWRP and after that a Custom ROM.

My question is simple... LGE LG D855... the international one, are the 16 gb and 32 gb versions the same regarding custom ROM´s? I just want to be sure, so that I don´t mess anything up.

[Q] What's the difference between the XT1575 and XT1572 regarding system image?

I live in Germany and will soon receive my style, maybe tomorrow. My question:

There are several issues, that points to different system images of the XT1572 and XT1575. I assumed, that for example the lte channels (= modem) are the only difference, but there are some others, too. In an other thread, an user described a problem with using WiFi correctly, after flashing the system image of the XT1575 on a XT1572.

This would result in different roms, if development will start soon. Is this correct? Does anybody know, what's the real difference of the two devices regarding software/hardware? Are there different WiFi modules? Can you please support me?

I'll wait with rooting my device until I'll get some clearance about this (and maybe until M via OTA arrives).