Are there specific commercial session IPAs that you like? If you can find a couple of "clone" recipes for those beers, that can often be a starting point for a first attempt at a recipe.
Using the Karma Citra ingredients list:
You could lighten the color and/or malty-ness by using
* Caramel 10 or 20, rather than Caramel 40.
* using 1 lb sugar rather than using 1 lb DME.
I haven't used Amarillo as a bittering hop and I have no experience with hops in the '@ 30' time frame - so I don't have anything to offer here.
If you're set up to do 1 gallon test batches, OG of 1.050 is 20 oz of DME (or a pound of DME and some sugar).