What should I look at when evaluating a company preIPO stocks

Im specifically looking at CASA Systems. Some of the calculations Im doing seem laughably horrible but Im thinking its because their IPO is Thursday, so for example theres millions of outstanding shares. Curious for tips on how to evaluate? Thanks for any info/help.

Total Revenue considered over at least 3 years, is it growing steadily Net, particularly if it is negative Source of operating cash, if it is borrowed, it is a red flag, if it is from cash coming in such as a membership fee much better Fundamental business, an airline has one set of risks, a marijuana grow has another, figure out how they make money What is their operating margin? Does growth take precedence over profit? You can add another dozen. Better yet, look up how Warren Buffett values a company and think how to adapt to your conditions.