I get some ingredients from Florida Aqua Farms such as bulk gelatin, vitamin mix, and spirulina powder. You shouldn't use more than 8-10% squid as it is very fatty and you can cause health issues if they get too much. I use about 40% white shrimp and smaller portions each of wild Salmon, mussels/clams, roe (from Asian market). I also add Salmon oil (squeezed out of gel caps), Selcon, and garlic extract.
I don't think adding a squeezed lemon would help much. Freezing it is just fine. I bag mine in Ziplock sandwich bags, then put two of those into a Ziplock freezer bag. As long as you sqeeze all the air out of the bags you won't get freezer burn, and don't make more than you can use up in 6 months.
FWIW, I've used this recipe for several years and I don't have any phosphate issues. I don't think
what you feed is as important as
how much you feed when it comes to phosphate. It is true though that some ingredients do have significantly more phosphate in them, but these ingredients aren't necessarily avoidable. Phosphorus makes up protein, so higher protein foods have higher phosphate.
Here's some reading by Randy Holmes-Farley (2012) on phosphate sources.
www.advancedaquarist.com/2012/3/chemistry