you are welcome

it is much easier to break a 5mm glass dangling in the middle  than an 8/10mm glass and it does not need to be 10cm wide... even 7cm is oK.. production aquariums have braces just 4 to 5 cm wide

I usually do the horizontal braces same thickness of the glass used or maybe 2mm less, however the cross braces can be thinner if you wish or keep them 8/10mm just for more strength.

as for braces on top, 2 are more than enough. even one would be great. normally we try not to separate the braces more than 60-70cm apart

well accidents do tend to happen unfortuantely and better be safe than sorry... however at 150cm length you should be fine...