Midnight blue might be easily noticeable upon daytime entry, and standing out like that is not ideal. (It's not like the hosts and many other guests would know that black should be reserved for evening.) Therefore, black would be safer.
The first model has a rather high heel. That might benefit a shorter man and might be bad for a tall man. Burgundy does exist for Gucci loafers, and that color has more potential for khakis/suits dual-use.
Don't order multiples from a brand not tried before. Have shirts from several different brands. (T.M. Lewin is another worthwhile option.) It can only hurt reputation to be the guy who seems to wear the same shirt every day Variety in brands, materials, etc. helps provide some visual variety. Of course so would color variety. Collar shape is dependent mostly on face shape. Without pictures, who knows.
Thank you. You probably are right that it's shotgun broguing. If it's the other possibility you state, the OP (unlikely to return) could refute if he finds that his pair has the same pattern as many other pairs of that model in other people's/site's pictures.
As suspected, it's probably ostrich.
Edit: if there's a model number, using Google or contacting the company likely will lead to confirmation.