Carful positioning of signs and the ANPRs themselves would be important. As suggested I guess the cameras would go mid bridge.
As for the height barrier it stops almost all overweight apart from the likes of Luxury SUVs. There is an issue with them having to turn around but that exists now. At least the height barrier can force the turn where as the bollards (judging by all the paint) may not.
Maybe ring fence the penalties until the cost of the system is repayed.
Like most things there is a balance as I think some would loose out. The Mercedes Sprinter type van seems like it would be under 3t but is very tall so wouldnt get under the barrier. I would hope during this consult they have decent vehicle data to weigh (

that up.