I did this project a few years back and must say I love my counters.
There is a book you can get from the library that will inspire you, Concrete countertops written by Fu-Cheng.
There was a little too much guidance for me though, He specified some additives to his concrete mix that I couldn't find so I ended up leaving them out. All of the ingredients for the concrete mix that I used I found at Home Depot.
I think 1" is too thin, my smaller pieces are 1.5" and the big piece which is 9' long has the sink cutout and weighs about 250lbs is 2.25" thick. I used rebar and remesh for support and molded them top side down in my garage. I built the mold from melamine and formed the edges with 2x4's that I covered with plastic tape so the wood grain doesn't transfer to the finished piece. Calk all the gaps with silicon and be neat because everything shows in the finish.
Mix your concrete with as little water as posable and vibrate it into the mold (I used a sawsall to shake the air out of the mold).
You need to let it cure for as long as posable maybe 3-4 weeks.
To finish I just sanded with a d/a sander, buffed and applied carnauba wax.


I'd be happy to answer any questions you have.