It's hard to say how long? Just think initially patience and good things come to those who wait.
Think of it this way. You are using an electrical process to remove material. The reason for circulation is as we remove material we want it to go somewhere even though they are micro particles. If the electrolyte doesn't flow then the material will begin to build up on our electrode. You will be plating sewing needles.
Not a big deal but eventually you will want to circulate the electrolyte and filter it.
As to the electrolyte? Yes, I suggest boring stuff like salt water and try a few concentrations. Electrolytes like this can also be acids or caustics at which point if something goes wrong you can be really hurt! Things like safety goggles and rubber gloves come into play. Just a tiny splash of acid or caustic can take away your vision for life. High price to pay for an experiment huh? I won't be the one to tell you just fill a beaker with 50% sulfuric acid and water and shove a few electrodes in it.
More advice, buy a small mountain or paper and a box of sharp pencils. When you try different electrolyte solutions take notes as to the salt added and volume of the solutions. Note currents and voltages, hell note everything as you muddle along. Collect and save your data. You are refining a process for your parts, your application.
When you get a process going look for tiny bubbles, they will be an indicator something is going on.
Just be safe!!!!!!
Ron