Bobby Kaucic

12U will work height wise, but as far as I know, the batteries are longer than the rack so they will stick out...

Check this thread, it speaks exactly about homing of 4 x US3000
 
 

Victron Multi II 5KVA, MPPT 250/85 with 12 panels and a 48V battery bank

My meter is a normal Hexing HXE310-P (three phase) and its not prepaid but pay as you go...they use this same meters for Prepaid...
I downloaded a manual for this meter and it can be configured to accept feedback for predefined amount of time and predefined max. W etc, but only distributors have the cable interface, software for it and most probably passwords 
 

I am actively watching this - but the news about it are scarce...

I secretly pray that COCT wins as doing so would open up the country electricity procurement to that path of normality.

Fingers crossed 🤞

Way too small. That's 60*50 = 3kW (just rounding the numbers to make the math easy). Also, the Multi can exceed 5kw for short periods of time. The fuse needs to be at least 125A as should the breaker.
The fuse and/or the breaker is there to protect the cable. That is all. A fuse cannot protect the electronics since it usually doesn't blow fast enough. What usually happens is the electronics blows up, causes some kind of short circuit (eg MOSFET that burns through) and that then causes the fuse to blow. If the fuse isn't there, then things get hot and you end up with a fire.
Your cable must be sized for 150A or so (35mm^2 or larger), and then I'd make the fuse even larger, 160A or 200A. Again, the fuse is there to protect the cable, and a cable of that size can hold that kind of current long enough to blow the fuse.
Also, refer to the Victron installation recommendations, which recommends a much larger fuse than I just did!
In your case, since there is a fuse and a breaker, I would not worry about the breaker too much. The fuse will tend to blow first anyway. Fuses blow within 10 seconds at twice their rated current (this depends on the type of fuse, fast blow fuses obviously blow faster). In your case the breaker is there only as a means to disconnect the DC, the fuse is the real overcurrent protection.