I think you may need a little more aeration in your mix. The ratio generally accepted in good quality soil is 20-30% aeration media such as perlite, lava rocks, buckwheat hulls, or rice hulls. Since you are using prepackage soil those will both have the proper ratios but when you added the vermiculite it kind of throws those ratios out a bit.
Do you intend to reuse this soil or will it be single runs? If you are reusing it I would suggest getting some long term nutrients in the mix such as crab meal, kelp meal, crushed or pulverized oyster shells and highly recommend some soft rock phosphate. Neem cake or meal will help with pest control and gypsum will help supply calcium, which is as important to me as NPK ratios and will also help improve the structure of the soil over the long term use. If you are going to trash the soil after ever grow then ignore all of the information in this paragraph as it won't apply much to single run soil.
Best of luck! Post a thread when you start using it so I can follow along.