There are other decisions you need to make such as bunks or rollers, SS disks, LED lighting, torsion or leaf springs, SS hardware, alloy wheels etc. To an extent, some of those decisions will be influenced by your usage, Maybe you will be operating in fresh water, maybe salt. Maybe you will take short runs to launch. Maybe you will launch and haul only a few times . Certain options add up fast
With respect to trailer size, don't undersize but also don't think that a larger(longer) trailer will be better. A too long trailer will make it hard to correctly balance your load. When sizing, too things are most important; grosss weight capacity and bow eye to transom length.
The comment about local dealers is somewhat important. You may be limited to your choices of manufacturers.
One idea might be to call your local Grady dealer and ask what they would provide for your model boat (basically, who do they deal with)