Agsil is potassium silicate, a.k.a Silica a.k.a Protekt. All the same thing, Agsil 16h is just the raw form. Mix it with water, make a 3% dilution and presto, you have Protekt.
I got some beans, chives, onions, garlic, oregano, basil, sage, kale, peas, lettuce and cilantro going right now. I like the idea of marigolds, should work. I'm going to get some sunflowers and pansy's going soon along with some other assorted flowers, that's my pest control this year. Keeps the bee's happy too. I just gave them their first AACT yesterday, some EWC and sucanat. Weather has been good, ever since I have got my greenhouse up we have had no rain, ironically. Winter, not so much. I was going to go with a hoop house but decided a metal frame is better for my situation.
I would make sure you make a sturdy frame, if you're getting a lot of heat. Hoop house's tend to warp like a mo'fo on a sunny day. I built some last year, with 1/2" pvc. First hot day I poke my head outside to look and the hoop houses were all hammahjang?! Looked like a PVC tumble weed blowing across the yard, I want to make some square foot gardens with PVC sometime. Next time I will use 3/4". Another reason why I got a frame from Home depot, after sketching up a blueprint for a good size pvc hoophouse, it's cheaper to just buy a frame. Mobile too. After this season is pau, clean it up, pack it, put it away for next season. I got some plastic from ace, it works okay but next time I'm going to do a little more looking around when I buy my plastic.
Whatever you end up making, for however much the cost is. I am sure you won't regret it. This is the best investment I've made this year.