what is a good amount of money to invest or start working in stock market?

Yes, this is a "good amount of Money" to invest more than adequate to start.

Your allocation to stocks, bonds, and cash depends upon your age, risk tolerance, and size of your investment portfolio.

This amount can earn about 6% per year annualized over some period of time.

I would recommend with this amount, all allocated to stocks, (that means you have other assets in cash and bonds), 10 companies each within a different sector for diversification. In other words, $10-15K invested in 10 different quality, dividend paying companies with proven earnings,increasing dividend history, manageable debts levels, and significant market share.

My choices would be:

answered in another question.

If it's money that you won't have to rely on to support yourself then put it all in a brokerage account. I use Tradeking because it has $5 trades. There's no reason not to start investing with all of your money. You can just create low-risk portfolio. Maybe invest 3/4 in a money market mutual fund or CD and the rest in the stock market to start. In all honestly, you should put it all in the stock market now. The recession has greatly lowered stock prices and they are basically on sale. In a few years you will be very happy you purchased while the market is down.