need a little advice on ABS wall thickness for my first project.

[curious aardvark]

it should bridge 30mm without any problem. the first layer will be a bit droopy. you can sand it flat.

Hmm, looking at the model - you've actually got one small suspended part - in the middle - and two very long parts either side.

you will need to use support.

But nothing complicated, so just use about 15% automatic support and it shoild be pretty easy to remove.

What slicer are you using ?
And what settings are you using for walls infill etc.
with 3 shells/layers and 25% infill AND the support it comes in at around 61gms. - 3 gms being the support.

And that would be pretty damn strong.