I had a 3.8m tinnie previously and although fishing the estuaries was doable, it wasn't too comfortable, especially if it was choppy.
Now with a 4.55 Quintrex escape runabout, inshore fishing with 3 people is very comfortable. Fishing headlands and the close reefs is comfortable as well.
I would recommend going for a boat around that 4.5m mark and the minimum i'd go is 4.2m, Anything smaller would be uncomfortable with 3 people.
Also you do not need a safety inspections if the trailer is less than 250kg tare weight, regardless of whether it is braked or not. So the boats that you are looking would not need a safety check for rego. https://www.service.nsw.gov.au/transaction/esafety-checks-pink-slips