You seem to be thrashing about, Vlad.
No i've already outlined in numbered points what the advantages of a British constitutional monarchy are over it's dismantlement and replacement. What we have not heard from the republican side is why and how the benefits of the British monarchy can and should be substituted with a republic.
That there are "benefits of a British monarchy" seems to be begging the question: for me, the key point of republicanism is to simply dispense with the archaic nonsense of the hereditary principle of monarchy, with all it's special privileges by dint of the presumed superiority of those born of certain parents.
Why for instance is democracy more fitting for ceremonial and non executive functions of state?
Personally I'm not certain that a ceremonial head of state is required: but if so, and we need someone to meet and greet, unveil plaques, cut ribbons and sign documents (that they cannot refuse to sign anyway) and wave when required - then if we elect someone and they turn out to be useless at these onerous tasks there will be an opportunity to either replace them of keep them in the role.
How does the election of a president improve our lot?
I'm not sure it does: but then I don't care for ceremony just for the sake of it.
How is historical continuity and our sense of nationhood preserved in and by a short term President with whom we cannot possibly develop any kind of respectful trust and sense of security with in a five year period?
Again; maybe we don't need such a person but provided they can shake hands, cut ribbons, sign documents (purely as window dressing), unveil plaques and, of course, wave when required without frightening children and small furry animals, then whether you chose to respect or trust them, or not, is of little importance since the role is just cosmetic window-dressing.
Until you put a case we don't know what a British presidency is for. There is no reason as in a newly independent state for a complete break from history, that which is elected is political.
Well I'm not sure that we need a "British presidency" at all, or a Scottish one in due course: for me disposing of the monarchy and all the frippery and nonsense that surrounds it, along with the House of Lords and the notion of an established church, would be enough.
Personally, since I don't see that a ceremonial President is required, then I'm not advancing the case of one.