Glad to see our advice helped your decision btw - hope you have a ton of fun, and don't be shy asking if you got any more questions! This thread probably helped more than one person.
I'm sure I will. Already very excited by the game and it's potential.
On the slot ranks then I think what I was getting at, in a roundabout muddled way, was that if you could bump up the rank of certain slots (so say improving the ensign slots to Lt.) then the extra abilities would potentially increase how long you could use a smaller tier ship.
Am I right in saying each ship type has a certain amount of bridge officer slots (say 2 tactical, 1 science and 1 engineering for T1 escort), and that each slot has a certain rank limit? So you might have one that you can have a Lt in, and the rest Ensigns. So all the ensign slots get to use one bridge officer ability and the Lt 2?
But if you put a Lt.Cmdr in the Lt slot they can still only use 2 abilities?
This is the one that is the real catch and something they should probably change. I suspect that this was done for ease of coding. Ideally the rank of your BOs would be based off your rank and not your ship tier.