First Mortgage Payment with first direct

KuchKuch

My mortgage is being drilled down on Friday, but I was hoping here somebody could confirm a few questions I had as first direct seem to be giving me mixed messages:

1. My mortgage with first direct is being drilled down on 30th June, with completion on 3rd July. My prepared payment date is the 25th of each month. With this in mind, would my first payment occur on 25th July?
2. My mortgage illustration document states that I "will have  24 payment(s) of £2,798.86". Therefore will my first payment by £2,798.86 or will this be slightly different for my first payment? If so, does anybody know how I can calculate what my first payment will exactly be?

Thanks.