I was too impatient to wait for the 64gb and I bought the 16gb as soon as I could get my hands on it. I too had some buyers remorse as I the only one that was available was black and I thought "If I am going to settle with the 16gb why not get the cyan". Anyway, I never filled the memory up, the only drawback of the 16gb is that you will be pretty limited if you plan to dual boot nemo on it. Eventually I bought a new casing and now it's cyan

Regarding sims I don't know if your carrier has this service but I've gone for a twin sim. That is two sims with the same number. I have used this service on two different carriers and here's how it works:

Carrier 1 (Cytamobile vodafone - Cyprus):
You can use only one phone at a time, you have to activate one of two sims by entering a hash code in the dialer and pressing "call" (IIRC #1301#). You receive an sms that your phone is active and can use it normally. When you decide to switch you do the same on the other phone

Carrier 2 (WIND Greece)
Both phones have signals simultaneously. The carrier rep said that you have to turn off (or put offline) the phone you don't use. My experience is a bit different. The last phone to turn on is the one that receives calls, with one catch, the first call gets rejected. So I just turn on my phone and call myself and I know that the phone I am holding is now active. You can do calls/sms/data from both phones at the same time.

Some other carriers have a 3rd option which is not in fact a twin sim, but another (hidden) number and cross-forwarding set up. This is not optimal as sms are not forwarded.