Tough questions! I'd think the answers are liable to be a matter of opinion, and therefore a bit vague.
My impression is that the trend is towards greater openness and more use of network opportunities. Excessive communication can become a problem, so it makes sense to consider whether an item needs to be passed to a wider group or not. On the other hand, my preference is to avoid being selective about any matter where all councillors may be interested.
Again, a personal opinion, but I am reluctant to create gatekeepers to decide what information should be exchanged between councillors. The clerk plainly has to filter the large amount of material that arrives at even very small councils, but it is not clear that this should extend to messages from councillors.
So, I'd be inclined to decide each case on its merits, but with a tendency towards openness and no restrictions imposed by other people.
Of course, if individual councillors say that they do not want to receive emails, then their views have to be respected, but that need not prevent exchanges between willing councillors.
As to predetermination, that is a particularly difficult issue, and one where legislation is promised. Simply discussing something does not appear likely to count as predetermination unless a strong view is expressed. Provided opinions are qualified by a willingness to entertain alternatives or to look at new information, there should not be a problem. And it would be very rare for anyone to formally challenge a local council decision on the basis of predetermination.