I think the best thing to do is go to a local marina and talk to them about that area. I have stopped at the Sebastian Inlet Marine for fuel several times. The folks there are very friendly and helpful and I am sure they can fill you in whatever information you want.
I've done a fair amount of fishing around there in my 19' CC fishing boat but the only experience I have there with my Carver is transiting the ICW.
I've been in the St. Sebastian River but not nearly as far as this property and I can tell you it gets very small and skinny back in there. But the fishing is fantastic. Also, as I recall, not too far into the river there's a RR bridge and I don't remember if it opens or not. I'm almost sure it doesn't and is quite low. (It's been a while since I was there last time) And there's a small airport there that may be annoying.
As for Sebastian Inlet, I went out it once a few years ago. (I was in a 20' fishing boat) I put it in a catagory very similar to Jupiter Inlet. I won't use it again. If I lived there and could get very familiar with it, maybe. But, Ft. Pierce Inlet is about 25 miles south on the ICW.
If you like to fish, that is a fantastic area.
Bob