What is the Return on Stake?
The typical ROS is 5.5% per year. Smaller pools, like AMKT1, do not mint block every epoch, but when it mints the returns are higher, because the rewards are shared with fewer delegators. Over time the return is like for larger pools. You can find information about the current performance of AMKT1 at adapools.org

What are the costs charged by ADAMarkets/AMKT1?
The fixed fee is 340 ADA, which is the lowest possible. The variable fee is 1%, of which ADAMarkets donates half to WRI.org.

How can I stake with AMKT1?
The easiest option is to delegate your Ada to AMKT1 stake pool by using either the Daedalus, Adalite, or Yoroi wallets.

Which pools are assigned to mint blocks?
The selection of pools to assign blocks is done about 1.5 days before the beginning of the next epoch. It depends on a number of parameters, e.g. pool size. You can read more about that here:
Pledging and rewards — Cardano Documentation 1.0.0 documentation

When do I receive my rewards?
You can find an explanation of the delegation cycle on the IOHK website.
In short the PoS protocol of Cardano, is as follows:

  • delegation during epoch N;
  • the first stake distribution snapshot is taken at the transition from epoch N to epoch N+1;
  • your stake produces rewards during epoch N+2;
  • rewards are distributed at the end of epoch N+3.

This means that first rewards are paid out three epochs after that you delegated to AMKT1, i.e. between 15 to 20 days.