With regard to Insurance, I doubt that the presence of BBQs etc would impact upon your Plan’s insurance cover, but that would depend upon the content of the Policy Disclosure Statement applicable to your Plan’s policy; you should read that.
Remember that the Model By-Laws only apply if they’ve been adopted by your Owners Corporation (O/C), and in any case By-Law 18 about the “appearance of the lot” is a little subjective, and is really more applicable to permanent alterations than it is to portable items such as BBQs.
If your O/C wants to manage BBQs and similar items purely from the perspective of fire safety and there are possible impacts at your Plan, then By-Law 11 may be of some benefit, but……
In my opinion, the best option would be for your O/C to manage the issue rather than to prohibit it, and the way to do that is for Proprietors to Specially Resolve (i.e. ≥75% in favour) at a General Meeting to create and register a Special By-Law to specifically manage the placement and use of BBQs / Gas Bottles / Gas Heaters on Lots.