Just started my first ever AG brew this morning, it is currently mashing (managed to hit 66C on my first try, very happy!)
I adjusted the recipe for my equipment and hops and it is:
Brewlength: 23L
4.12Kg Marris Otter
480g Crystal Malt
90 Min mash @ 66C
90 Min boil
35g Challenger (6.5% AA) for 90 mins
20g Challenger (6.5% AA) for last 15 mins
Beersmith is telling me it will have an IBU of 30 which seems spot on.
I have added a few pics below, more to follow as the day progresses.
Three tier system:

Grain bill:

Mash @ 66C:

G.