There is no limit to the number of browsers you can use. In fact, you can use as many browsers as your hard drive can hold. Often, developers use multiple browsers to test their codes online. They have installed Chrome, Firefox, opera, Vivaldi, safari, internet explorer, UC browser and edge simultaneously.
It really depends on your CPU if it can take up the different browsers at the same time. Hence, there is no limit to the number of browsers you can download. This is a real advantage for users as it opens the variety and gives you a true choice of browser rather than limiting your preference.