For stocks traded on the secondary market, there are generally no minimum order amounts. For the initial offering they’re usually presented in lots. There is a maximum number of stocks that can be bought, and that depends on the number of stocks on offer, and the price you’re willing to pay.
If you want to sell stocks, it again depends on market conditions and in some cases you might have to accept a loss in order to sell them. Either because no-one is buying or because everyone is selling.
This ease of buying or selling is called liquidity.
With bonds it’s a different story. Because of historical reasons, bonds are usually priced at $100 (regardless of face value) and bundled into packets of $500,000 on the wholesale market. So until now have only been available directly to the big investment institutions and banks in the over-the-counter market. These institutions and banks would often then package different bonds together and sell these packages to you in the form of shares. You would then be charged fees for management of these packages. So while the bond might return 6%, you only see a 4% or less return.
Selling bonds is a little different than selling stocks. Unlike stocks, bonds will return expected value plus interest at a specific date and that doesn’t change. And while they do fluctuate in what you can buy or sell them for, it’s usually on a weekly or longer timeframe, and rarely more than a few percentage points of the face value. You do still have to find a buyer, but it’s usually much easier to find someone to buy real value rather than some unknown expected return.