Do not let these pots freeze though. The concrete will absorb water, and freezing and thawing will cause the concrete to break, just like cheap ceramic pots that are left outside. Concrete is much mroe porous than ceramic though, and roots can grow into the crevices of the inside of the pots. So that will be something to watch out for.
Sanding them will not do much, as concrete does not sand well. It needs to be trowelled to a nice finish while it is wet and setting.
I work with cements and mortars, as I am a tile and stone setter. The acrylic admix will help the pot have some flexability to handle the expansion and contraction of the cement through temp swings, but will not make it freeze thaw stable.
I love seeing people do DIY projects. You should look into a local junior college, or ceramic shop, or pottery shop. You can usually either join a club, take a class, or pay a small fee to use their kiln. Then you can use ceramic or porcelain clay and make your own pots with help and advice from others. It is always fun to create something with your hands. Best of luck, keep posting updates on your pots as you finish them and as they wear. I am interested to see how they hold up.