Hi, Rod, I'm new, too, to EarthBoxes and also the forum. I had already mixed up my peat moss at about 80% and added both vermiculite and perlite at 10%, but I began questioning myself when I read some posts where people were having trouble with their homemade mixes, and the responses were to buy a suitable mix at the store. So I emailed EarthBox customer service, and the response was to use the peat and perlite, not the vermiculite. But since I didn't want to waste the mix I had already blended (and because it was a lot of trouble and pain for my old back), I went ahead and filled up my first box with what I had made. I have 8 lettuces in it that I grew from seed, and they're doing great so far.
I did order four more boxes which came this morning, and I'll probably go with perlite and not add the vermiculite to the mix this time. Vermiculite holds water, but perlite makes the mix lighter so it keeps the medium from getting soggy and prevents smothering the roots. I just checked Home Depot, and they have a 2 cu. ft. bag (Vigoro) for $17.97, or an 8-qt. bag (Miracle-Gro) for $5.37, plus others. To answer your question, I think you would be better off using the perlite if you can find it or order it. Without it, you may have an overwatering problem.
Good luck and happy gardening!