Full disclosure, although I've transited a number of inlets up and down the coast, I've never transited St Mary's inlet. So these are just my thoughts and worth roughly what you are paying for it :-) (perhaps less?)
I took a look at the inlet on active captain:
To me it looks to me like it *can* get nasty when current is against wind. And that curve in the inlet suggests that the current will set such that you will tend to drift towards one jetty or the other.
Here is some of of what Active Captain has to say about the inlet:
The mean range of tide is 5.8 feet at the entrance and 6 feet at Fernandina Beach. The tidal currents at the entrance have considerable velocity and are dangerous at times, especially on the flood which generally sets northwestward and on the ebb which sets southeastward except during northeast winds when there is a strong southerly set off the end of the jetties on both tides. It has been reported that this set sometimes attains a velocity exceeding 5 knots
. Maximum current velocities are reported to be 2.0 to 3.9 knots in St. Marys Entrance and 1.0 to 2.5 knots in the Cumberland Sound channel.
Those are some pretty strong currents. Based on what I have seen at other inlets I'd suspect that currents like that can set up some impressive (and possibly dangerous) conditions at times.
btw a great resource is the Inlet Chartbook: https://www.amazon.com/Inlet-Chartbo.../dp/0932265774
I dont think any of this is a deal breaker but I would treat that inlet with a lot of respect and pay close attention to the wind and current on the days you choose to transit. As you approach take some time to read the inlet. Use extra care when returning from sea since you will be observing the backs of the waves making it a little harder to get a good read on the sea state in the inlet from that position.
I think its good practice to require everyone on board to wear a life vest and be clipped in during the transit of the inlet.
You will be solo so surely you have that covered.
and since you are considering a bigger boat, I'd suggest that you rule out boats with an outboard. An outboard can pop out of the water in the very sharp, steep waves that can set up in an inlet. you will want an inboard that will put all the power you have to use.
be careful, sensible and pay careful attention and you will be fine.