Hello all,
I am working on trying to brew up a West Coast IPA clone from this recipe -
I only have an 8 gallon kettle, as I do BIAB, and would like to scale the recipe back a bit.
What is the best way to do so? What variables will I need to keep track of?
Any help would be great!!! 
Do you use brewing software? Use the same ratios of all the ingredients but scale them down based on your efficiency and batch size. Once you have your estimated OG on par I would adjust the hop amounts down to meet your IBUs.
Someone else here probably has a easier suggestion…
If you only have an 8 gallon kettle it appears, without doing the math, that you would need to essentially halve (or 1/4) the recipe. With the 90 minute boil and amount of hops it appears the creator accounts for almost 2 gallons of boil off and trub loss (5.5 into primary, 5 gallons finished volume). Brewing software would make this an easy deal as you can create your equipment profile and then easily scale any recipe regardless of size.
That’s how I do it too. Grains can be scaled down using a spreadsheet, but hop calculation is not completely linear.
Doesn’t Brewer’s Friend (the site OP linked) have that feature?
Yep, just copy the recipe to your profile, then scale it to whatever batch size you’d like.