Ok so you've got Brewmate working, which is a big help, but you need to change the recipe a little.
For the grains you'll want mostly base malt(in your case Maris Otter), something like 80-95% of the grain bill. The low numbered Crystal Malts, like the Crystal 10, are good for body and head retention. Having said that, you don't want to use too much Crystal Malts as they also give the beer caramel flavour and a sweetness, too much will make the beer undrinkable. So keep them to an absolute maximum of about 15-20% of the grain bill, in this case probably less than 10% is best.
The hops. Usually the hop additions are given in terms of minutes from the end of the boil rather than minutes into the boil. For example, the first addition will often be just as the boil begins and is used to give bitterness. If it is a 60min boil(which is typical) then this addition is denoted as the 60min hop addition. Obviously the hop addition right at the end of the boil is denoted as the 0min addition and is used to give hop aroma. Brewmate also uses this timing convention. Your Northern Brewer should be the 60min addition and the Citra should go in right towards the end of the boil, something like 10 or 5mins and again at 0mins, and perhaps as a dry hop too. That way you get lots of citrus flavours.
Your bitterness(13.4 IBU) is a little low for the style of beer you are going for. What you seem to be making is either an American Pale Ale, or more likely a British Golden Ale(a little less hops and alcohol than an APA but a bit more malty with some yeast character too), so you want your IBU number to be in the range 20-45 perhaps. Once you enter the style of beer you are making Brewmate will guide you as to the typical alcohol strength, bitterness and colour. If you stray outside the guidelines you will see yellow boxes light up. Sometimes you will find that you do stray a little over, for example a little darker or lighter, a little more or less alcohol etc. and you shouldn't worry too much about it, they are just guidelines after all.
I made a few 1 gallon batches and overall it was good experience. You get to brew often without building up huge stocks and certainly bottling is quick. The bad side is that it can actually be more difficult than brewing a bigger batch. There is less room for error with a small batch. Keeping the mash at a constant temperature is probably the main difficulty. Having said that, if you can brew a good 1 gallon batch then you'll have no problems when you move up to bigger batches.
Enjoy
