Weaf

Good evening all. New here and looking for some advice on a porch I’m planning to build. The porch will be block built with a 100mm cavity. I have already bought a composite door at 900mm wide and planning on purchasing uPVC double glazed window next. What I would like some advice on is what would the size of largest window would be that would realistically fit on the same aspect. I have attached a rough scaled drawing of the front face of the porch where the door and window will both be. I also wanted to ask: Is there a minimum distance advised between window and door frames as to not interfere with the integrity of the wall? ( A) and secondly, is there a standard distance from the top of a door frame to the level of the soffit? (B). (The roof will be 30 degree pitched with tiles.) My dad is a retired bricky who has kindly offered to do the block work. At nearly 80 he is very vague when it comes to rules and probably hasn’t refreshed his knowledge of building regs since the mid 60’s! Any advice is really appreciated to keep my dad in check once he starts wielding his trowel around! (the external porch dimensions are W 3700 x 1300 front to back) Many thanks in advance, Paul. W