Acrylic admixes in general will improve strength (resistance to cracking) and reduce curing time. I wouldn't worry too much about them reducing permeability. You really need to use the admix with a sealing product to produce an impermeable surface. What do you want to make that needs to be permeable? The permeability is the main thing that means hypertufa crumbles eventually, but it isn't permeable enough to use as a planter without additional drainage holes.

Leaching should not be an issue. If the lime doesn't leach out then it isn't a problem. Any piece of cement contains leftover lime internally, it is only the lime that reaches the surface that you need to worry about.

Normally the admix would be mixed into water and then mixed with the dry ingredients, but I know people here have done everything up to using pure admix and no water. I'll let them describe the results.

You can make any cement product as long as it is not freezing. The colder it is the longer it will take to cure. Below about 40F you will be waiting a week just to be able to take the piece out of the mould. Curing more slowly gives a stronger result but the most important thing is for the piece to be damp or wet at all times. Admixes make curing faster without losing strength.

You can use any aggregate that you like, providing it is inert and hard. Reactive aggregates are sometimes used and sometimes even make the piece stronger but you need the right kind of reaction. Glass has been used as an aggregate for decorative pieces but is not used in structural work because the alkali dissolves it and weakens the piece. Weak aggregates can be used to reduce weight but you lose strength.

thank you for the very informative response! i am just making a planter, so now it's clear to me that drainage holes are essential. i actually went out and experimented in the garage just last night. right now i've got two castings curing in molds in my bathroom tub. They're both wrapped in plastic bags. i used 2 parts peat, one part portland, one part perlite, and one half part sharp sand. i mixed the dry stuff as well as i could, even using an electric-drill attachment mixer. then i added just enough acrylic/water solution (ratio 2/3 cup acrylic admix to 1 1/2 cups water)to get it all wet. i coated the molds and some dowels in a petroleum release agent and packed the mix into the molds. then i inserted the dowels. i sprayed the curing molds with water once today and wrapped them back up in plastic. i was told to spray them with water once a day for a week before removing the castings from the molds. does that sound slow to you? It's 70 plus degrees in my home. Maybe the planters are ready right now..