Is this consumer unit wired safely?
1) Yes, your interpretation of the layout and markings seems to be correct.

2) No, it's not a problem, it's a very typical setup. You can have breakers totalling more than the total capacity of the unit, on the ground that you are unlikely to be running each circuit at or near capacity at the same time.

A MCB (or RCD, fuse, etc) is designed (and sized) to protect "downstream" of it, not those "upstream". Ie the 6A breaker on the left of the consumer unit above is there to protect the 1mm^2 or 1.5mm^2 cable that is connected into it, as those cables can safely handle a 6A load. They aren't there to protect devices further upstream.