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Paul,
The short answer is that (ignoring the Body Corporate / Safe Handling issues) your design concept could in theory be made to work, but it could be problematic for photography work, due to the likely vibrations that you would get from building vibrations, gusts of wind, etc. The member sizes are OK to carry the loads, but vibrations for a bracket of this type (especially twisting of the arm, leading to sway at the top plate) could be a problem, to keep the deflections of the scope down to arc-second accuracy and stability that you want for astro-photography.
1 & 2: Body Corporate: I would seek permission - it is a pretty small unit block and a pretty small Body Corporate. My main concern is: Would weakening the column be an issue with drilling 2 or 3 holes? We are on the top floor (only 3 levels) and the column has done nearly all of its work by the time it gets to us - it's really just holding up that edge of the roof. Tell me, please, if you think I am wrong about this.
Drilling into concrete is fine in principle, as long as you try to miss all of the rebar - but only if the Owner / Body Corporate approves.
3: You are quite right about 30 kg loads - manhandling that mass would be tough. However, it is only 3 separate sets of 10 kg. First, I would instal the mount (10 kg), then the counterweights (10 kg) and finally the scope (10 kg). I think lifts of 10 kg are probably manageable?
While you or I could probably manage the task if we had to do it occasionally, safe work practices would suggest that manual handling of 10 kg loads at an outreach of 600 mm or so beyond a parapet is a non-no - risk of back strain, risk of dropping the load, etc. (The Body Corporate's concern will be the risk to other occupants and property if the load falls - they won't care about the cost of the dropped scope or mount!)
4. It is for photography only. The scope will carry a DSLR which I will use to capture images.
Astro-photography demands an exceptionally stable mount; cantilever brackets are notorious for being prone to sway and twisting deflections and vibrations.
To have any chance of success, the fixing to the concrete wall needs to be REALLY rigid. I would suggest a side-plate connection using Masonry Anchors (Ramset or Chemset type) into the concrete as per the attached sketch, rather than the "Through Bolts" in your sketch - but the Body Corporate would almost certainly object to these sorts of fixings.
As for how you would go about getting Body Corporate approval to install something like this, and how you would address the personal injury risk to yourself and others - well, I'm afraid I don't have any suggestions there!
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