I don't know why you couldn't use SRF in your recipe. The best policy regarding amounts is to pretty much follow the directions (or less) for your particular product. What kind of plants are you going to be growing in this mix?

There are hundreds of different kinds of fertilizers on the market. You will simply have to find one that provides your plants with what they need. If you plan on keeping plants in this mix for a long time, I urge you to find something with the minor elements included. NPK alone will not supply the trace elements.

I think you should know that vermiculite collapses very quickly and will not add the structure and porosity that I assume you're looking for. It turns into mush. If you want something which increases porosity, provides lots of air pockets, holds onto a fair amount of water, and is sturdy enough to do its job for a long time.....perlite is what you want.