I tend to agree, in addition to the modernity and design of the stadium, the most important thing is atmosphere and we want to make it as intense and intimidating as possible and have the crowd packed in, as close on all sides to the pitch as possible, in the traditional English manner.
In general I think, for each 5k increase in capacity above 50k, you probably lose a degree of that atmosphere and intensity. I like The Emirates as a stadium, but I certainly wouldn't class it as intimidating, and as one of the modern stadia, its nothing special IMHO. We have a real opportunity here to do something unique and iconic, learning from the other clubs and avoiding their formulaic designs. I assume that costs additional money though, and the priority is getting this built and functional.
I don't think they will go as "low" as 45,000 but 50,000-52,000 with capacity for more in the future is where I would see it, just to cover our bases for maximisation of revenue and flexibility.
I know nothing about stadium design and construction, but you would think in this day and age that its feasible to come up with a design that allows for closure of upper-tier seating in such a way that empty seats are not as noticeable, and/or can be sealed off as it were from the rest of the ground by means of shifting stand covers (i.e. up and down)? There is a much less sophisticated model of this in the MLS for Vancouver Whitecaps - I don't know the stadium name but they attempt, rather crudely, to cover off the top/upper-tier seating with tarpaulin, to give the impression of full capacity. I wonder can a more aesthetic solution be engineered into the initial design much like the basic concept that is applied to retractable roofing?